[llvm] [compiler-rt] follow-up to 166837, rename COMPILER_RT_FORCE_TEST_BUILTINS_DIR to COMPILER_RT_TEST_BUILTINS_DIR (PR #171741)

[Andrew Haberlandt via llvm-commits]

https://github.com/ndrewh approved this pull request.

Thanks for this. Sorry I missed the rename. I think I just hit the "replace all" button in VS code but I had the filter set to `compiler-rt`.

Sorry!

https://github.com/llvm/llvm-project/pull/171741