[Tests] Properly link Linux tests
[Tests] Properly link Linux tests

https://github.com/apple/swift-corelibs-xctest/pull/46 is missing
this change to the compiler invocation, which allows tests to run
on Linux even when `--library-install-path` and
`--module-install-path` are not specified.

yoonapps/swift-corelibs-xctest,yoonapps/swift-corelibs-xctest,tiagomartinho/swift-corelibs-xctest,apple/swift-corelibs-xctest,tiagomartinho/swift-corelibs-xctest,apple/swift-corelibs-xctest