Issue Description:

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

******************** TEST 'lldb-Suite :: lang/swift/reference_storage_types/TestSwiftReferenceStorageTypes.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/reference_storage_types -p TestSwiftReferenceStorageTypes.py
Change dir to: /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/reference_storage_types
UNSUPPORTED: LLDB (/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7-ppc64le) :: test_swift_reference_storage_types_dsym (TestSwiftReferenceStorageTypes.TestSwiftReferenceStorageTypes) (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/reference_storage_types -C /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/reference_storage_types/TestSwiftReferenceStorageTypes.test_swift_reference_storage_types_dwarf -I /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/reference_storage_types -f /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/reference_storage_types/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: 25263
stdout: make: Entering directory '/home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/reference_storage_types/TestSwiftReferenceStorageTypes.test_swift_reference_storage_types_dwarf'

Compiling /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/reference_storage_types/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/reference_storage_types/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 / -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/reference_storage_types/TestSwiftReferenceStorageTypes.test_swift_reference_storage_types_dwarf/main.partial.swiftmodule
-o /home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/reference_storage_types/TestSwiftReferenceStorageTypes.test_swift_reference_storage_types_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 / -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/reference_storage_types/TestSwiftReferenceStorageTypes.test_swift_reference_storage_types_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/reference_storage_types/TestSwiftReferenceStorageTypes.test_swift_reference_storage_types_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/reference_storage_types/TestSwiftReferenceStorageTypes.test_swift_reference_storage_types_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 "/" -o "a.out"
make: Leaving directory '/home/sar/swift-source/build/buildbot_linux/lldb-linux-powerpc64le/lldb-test-build.noindex/lang/swift/reference_storage_types/TestSwiftReferenceStorageTypes.test_swift_reference_storage_types_dwarf'

stderr: /home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/reference_storage_types/main.swift:28:7: warning: variable 'myclass' was never mutated; consider changing to 'let' constant
var myclass = MyClass()

let

retcode: 0


runCmd: frame variable myclass.sub_001
output: (a.Minion?) myclass.sub_001 = (x = 1) {
x = 1
}


Expecting sub string: x = 1
Matched

runCmd: frame variable myclass.sub_002
output: (a.Minion?) myclass.sub_002 = (x = 8589934598) {
x = 8589934598
}


Expecting sub string: x = 1
Not matched

FAIL: LLDB (/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7-ppc64le) :: test_swift_reference_storage_types_dwarf (TestSwiftReferenceStorageTypes.TestSwiftReferenceStorageTypes)
<bound method SBProcess.Kill of <lldb.SBProcess; proxy of <Swig Object of type 'lldb::SBProcess \*' at 0x3fff8b046f30> >>: success

UNSUPPORTED: LLDB (/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7-ppc64le) :: test_swift_reference_storage_types_dwo (TestSwiftReferenceStorageTypes.TestSwiftReferenceStorageTypes) (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_swift_reference_storage_types_gmodules (TestSwiftReferenceStorageTypes.TestSwiftReferenceStorageTypes) (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_swift_reference_storage_types_dwarf (TestSwiftReferenceStorageTypes.TestSwiftReferenceStorageTypes)
Test weak, unowned and unmanaged types
----------------------------------------------------------------------
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/reference_storage_types/TestSwiftReferenceStorageTypes.py", line 32, in test_swift_reference_storage_types
self.do_test()
File "/home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lang/swift/reference_storage_types/TestSwiftReferenceStorageTypes.py", line 69, in do_test
self.expect('frame variable myclass.sub_002', substrs=['x = 1'])
File "/home/sar/swift-source/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 2388, in expect
msg if msg else EXP_MSG(str, output, exe))
AssertionError: False is not True : 'frame variable myclass.sub_002' returns expected result, got '(a.Minion?) myclass.sub_002 = (x = 8589934598) {
x = 8589934598
}'
Config=ppc64le-/home/sar/swift-source/build/buildbot_linux/llvm-linux-powerpc64le/bin/clang-7
----------------------------------------------------------------------
Ran 4 tests in 1.164s

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