[Tests] Set LD_LIBRARY_PATH when running tests

[modocache]

swiftlang/swift#2609 introduced a change to the default behavior of the Swift driver, which now uses the gold linker unless specified otherwise. This caused a linker error in swift-corelibs-xctest's test suite, which this commit fixes.

/cc @compnerd -- does this seem like a reasonable fix? To be honest, I'm not sure why such a change would be necessary for gold but not bfd.

[modocache]

@swift-ci please test

[ddunbar]

This doesn't feel right to me, I'm not sure why clients should be expected to change as a result of that PR.

[modocache]

I wonder if the real issue has more to do with swift-corelibs-foundation and how it packages libFoundation.so, as opposed to the library search paths our tests use at runtime. I'm still looking into it.

How would you feel about merging this as a short-term fix? I feel bad having broken @rintaro and @RLovelett's builds. 😞

[compnerd]

This is okay to do. However, I think it would be better to just embed an DT_RUNPATH in the test binaries as they are tests. (--enable-new-dtags --rpath /path/to/libraries).

[modocache]

The Foundation failure is preventing the Linux tests from running on CI, so we don't have a ton of visibility into how this affects the Linux build. That being said, I can assure you that this "works for me" 😁

[modocache]

Created a task to track uncovering why this change was needed: SR-1625. For now, I'll merge this and unbreak @rintaro and @RLovelett's builds.