relates to:

• SR-5467 The .build/debug symlink doesn't work for SwiftPM development

Issue Description:

SwiftPM Development.md states that the following should work:

$ cd /tmp && mkdir hello && cd hello

$ /path/to/swiftpm/.build/debug/swift-package init

$ /path/to/swiftpm/.build/debug/swift-build

However, in recent (yesterday's master) SwiftPM this fails with:

sbs:/tmp$
cd /tmp && mkdir hello && cd hello
sbs:/tmp/hello$
/tmp/swiftpm-proj/.build/debug/swift-package init
Creating library package: hello
Creating Package.swift
Creating README.md
Creating .gitignore
Creating Sources/
Creating Sources/hello/hello.swift
Creating Tests/
Creating Tests/LinuxMain.swift
Creating Tests/helloTests/
Creating Tests/helloTests/helloTests.swift
sbs:/tmp/hello$
/tmp/swiftpm-proj/.build/debug/swift-build
error: manifest parse error(s):
/tmp/hello/Package.swift:4:8: error: no such module 'PackageDescription'
import PackageDescription
^

This is because search paths are set in such a way, that `lib` dir is expected to be next to `debug`.

The following works:

sbs:/tmp/hello$
/tmp/swiftpm-proj/.build/x86_64-unknown-linux/debug/swift-build
Compile Swift Module 'hello' (1 sources)

Or, likely better solution:

sbs:/tmp/libtest (master)$
cd /tmp/swiftpm-proj/.build/
sbs:/tmp/swiftpm-proj/.build (emit-library-instead-of-x-linker-shared)$
ln -s /tmp/swiftpm-proj/.build/.bootstrap/lib

sbs:/tmp/swiftpm-proj/.build (emit-library-instead-of-x-linker-shared)$
cd /tmp/hello/

sbs:/tmp/hello$
/tmp/swiftpm-proj/.build/debug/swift-build
Compile Swift Module 'hello' (1 sources)