fix SR-1109: don't use the clang resource override dir for glibc

[tfiala]

Fixes SR-1109.

Reviewed by: Jordan Rose

We were using the clang resource override dir in a place where it shouldn't be used. LLDB (and thus the REPL) is the only consumer of this feature. It is meant for clang modules.

[tfiala]

@swift-ci Please test

[tfiala]

Okay, we're now hitting a bunch of errors in the LLDB suite, so this isn't quite right yet.

[tfiala]

The LLDB REPL test failures go away if we use the package-layout LLDB for the LLDB executable, but the LLDB REPL tests fail with the in-build-tree layout that used to work.

We hit asserts on many other Swift tests in the test suite regardless of the layout of the binaries. I'll be looking into those.

[tfiala]

I just put in a dependent LLDB change here:
apple/swift-lldb@ea2a5f2

This fixes an issue where Swift modules were not necessarily setting their resource dir. The fix for this PR unmasks that we were in this scenario, which would have caused asserts in the LLDB test suite without addressing the underlying cause first.

[tfiala]

@swift-ci Please test Linux platform

[tfiala]

The only failure in the build on Linux was the integration test that I previously XFAILed because we didn't have this change in. There is no way to change that without breaking something temporarily (i.e. if I check in the integration test first, then they will fail until this goes in; similarly, if I check this in, the packaging will fail on the unexpected success as it did in this check here).

I'll adjust the integration test first and restart the CI if it beats me to this PR submission here.

[tfiala]

@swift-ci Please test Linux platform