Issue Description:

Failure of test case lang/swift/unknown_self/TestSwiftUnknownSelf.py on PPC64LE while building Apple Swift 5 toolchain.

******************** TEST 'lldb-Suite :: lang/swift/unknown_self/TestSwiftUnknownSelf.py' FAILED ********************
lldb version 7.0.0 (https://github.com/apple/swift-lldb.git revision c4fac5fb6378aabe7a46d367112894811e344f98)
Swift version 5.0-dev (LLVM 40e9a1bc2b, Swift 52ddabe)
LLDB library dir: /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/bin
LLDB import library dir: /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/bin
Skipping following debug info categories: ['dsym', 'gmodules']

Session logs for test failures/errors/unexpected successes will go into directory '/home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-traces'
Command invoked: /home/sar/swift-source/lldb/test/dotest.py -q --arch= -s /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-traces --build-dir /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex -S nm -u CXXFLAGS -u CFLAGS --executable /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/./bin/lldb --dsymutil /home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/./bin/dsymutil --filecheck /home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/./bin/FileCheck -C /home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang --swift-compiler /home/sar/swift-source/build/buildbot_linux/swift-linux-powerpc64le/bin/swiftc --swift-library /home/sar/swift-source/build/buildbot_linux/swift-linux-powerpc64le/lib/swift --env ARCHIVER=/usr/bin/ar --env OBJCOPY=/usr/bin/objcopy --build-dir /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex --test-subdir lang/swift --skip-category=watchpoint --skip-category=dwo -t -E -Xcc -F/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le/CoreFoundation-prefix/System/Library/Frameworks -I/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le/swift -I/home/sar/swift-source/swift-corelibs-libdispatch -L/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le -L/home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le -L/home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le/src -Xlinker -rpath -Xlinker /home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le/src -Xlinker -rpath -Xlinker /home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le -Xlinker -rpath -Xlinker /home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/unknown_self -p TestSwiftUnknownSelf.py
Change dir to: /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/unknown_self
UNSUPPORTED: LLDB (/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7-ppc64le) :: test_unknown_self_objc_ref_dsym (TestSwiftUnknownSelf.TestSwiftUnknownSelf) (test case does not fall in any category of interest for this run)
runCmd: settings set symbols.clang-modules-cache-path "/home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/module-cache-lldb"
output: None

runCmd: settings set symbols.enable-external-lookup false
output: None

os command: make VPATH=/home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/unknown_self -C /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/unknown_self/TestSwiftUnknownSelf.test_unknown_self_objc_ref_dwarf -I /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/unknown_self -f /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/unknown_self/Makefile MAKE_DSYM=NO ARCH=ppc64le CC=/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7 SWIFTC=/home/sar/swift-source/build/buildbot_linux/swift-linux-powerpc64le/bin/swiftc
with pid: 26721
stdout: make: Entering directory '/home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/unknown_self/TestSwiftUnknownSelf.test_unknown_self_objc_ref_dwarf'

Compiling /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/unknown_self/main.swift

/home/sar/swift-source/build/buildbot_linux/swift-linux-powerpc64le/bin/swift -frontend -c -primary-file /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/unknown_self/main.swift

-g -Onone -serialize-debugging-options -module-cache-path /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/module-cache-clang -sdk / -Xcc -F/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le/CoreFoundation-prefix/System/Library/Frameworks -I/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le/swift -I/home/sar/swift-source/swift-corelibs-libdispatch -L/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le -L/home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le -L/home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le/src -enable-anonymous-context-mangled-names -module-name a -emit-module-path
/home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/unknown_self/TestSwiftUnknownSelf.test_unknown_self_objc_ref_dwarf/main.partial.swiftmodule
-o /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/unknown_self/TestSwiftUnknownSelf.test_unknown_self_objc_ref_dwarf/main.o

Merging swift modules for a

/home/sar/swift-source/build/buildbot_linux/swift-linux-powerpc64le/bin/swift -frontend -g -Onone -serialize-debugging-options -module-cache-path /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/module-cache-clang -sdk / -Xcc -F/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le/CoreFoundation-prefix/System/Library/Frameworks -I/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le/swift -I/home/sar/swift-source/swift-corelibs-libdispatch -L/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le -L/home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le -L/home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le/src -enable-anonymous-context-mangled-names -merge-modules
-emit-module main.partial.swiftmodule
-emit-parseable-module-interface-path /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/unknown_self/TestSwiftUnknownSelf.test_unknown_self_objc_ref_dwarf/a.swiftinterface
-parse-as-library -sil-merge-partial-modules
-disable-diagnostic-passes -disable-sil-perf-optzns
-module-name a
-o /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/unknown_self/TestSwiftUnknownSelf.test_unknown_self_objc_ref_dwarf/a.swiftmodule

Wrapping swift module

/home/sar/swift-source/build/buildbot_linux/swift-linux-powerpc64le/bin/swift -modulewrap a.swiftmodule -o /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/unknown_self/TestSwiftUnknownSelf.test_unknown_self_objc_ref_dwarf/a.swiftmodule.o

Linking a.out

/home/sar/swift-source/build/buildbot_linux/swift-linux-powerpc64le/bin/swiftc a.swiftmodule.o main.o -Onone -Xfrontend -serialize-debugging-options -module-cache-path /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/module-cache-clang -sdk "/" -Xcc -F/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le/CoreFoundation-prefix/System/Library/Frameworks -I/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le/swift -I/home/sar/swift-source/swift-corelibs-libdispatch -L/home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le -L/home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le -L/home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le/src -Xlinker -rpath -Xlinker /home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le/src -Xlinker -rpath -Xlinker /home/sar/swift-source/build/buildbot_linux/libdispatch-linux-powerpc64le -Xlinker -rpath -Xlinker /home/sar/swift-source/build/buildbot_linux/foundation-linux-powerpc64le -o "a.out"
make: Leaving directory '/home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/unknown_self/TestSwiftUnknownSelf.test_unknown_self_objc_ref_dwarf'

stderr:
retcode: 0

FAIL: LLDB (/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7-ppc64le) :: test_unknown_self_objc_ref_dwarf (TestSwiftUnknownSelf.TestSwiftUnknownSelf)
<bound method SBProcess.Kill of <lldb.SBProcess; proxy of <Swig Object of type 'lldb::SBProcess *' at 0x3fff6cf65e10> >>: success

UNSUPPORTED: LLDB (/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7-ppc64le) :: test_unknown_self_objc_ref_dwo (TestSwiftUnknownSelf.TestSwiftUnknownSelf) (test case does not fall in any category of interest for this run)
UNSUPPORTED: LLDB (/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7-ppc64le) :: test_unknown_self_objc_ref_gmodules (TestSwiftUnknownSelf.TestSwiftUnknownSelf) (test case does not fall in any category of interest for this run)
Restore dir to: /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/test-results

FAIL: test_unknown_self_objc_ref_dwarf (TestSwiftUnknownSelf.TestSwiftUnknownSelf)
Test unknown references to Objective-C objects.

Traceback (most recent call last):
File "/home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 1766, in test_method
return attrvalue(self)
File "/home/sar/swift-source/lldb/packages/Python/lldbsuite/test/decorators.py", line 145, in wrapper
func(*args, **kwargs)
File "/home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/unknown_self/TestSwiftUnknownSelf.py", line 51, in test_unknown_self_objc_ref
self.check_class(var_self, broken=True)
File "/home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/unknown_self/TestSwiftUnknownSelf.py", line 30, in check_class
lldbutil.check_variable(self, m_string, summary='"world"')
File "/home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lldbutil.py", line 1320, in check_variable
valobj.GetSummary() if valobj else ""))
AssertionError: False is not True : expected summary: '"world"' - actual summary: 'unable to read data'
Config=ppc64le-/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7

Ran 4 tests in 2.111s

RESULT: FAILED (0 passes, 1 failures, 0 errors, 3 skipped, 0 expected failures, 0 unexpected successes)