[compiler-rt] [llvm] [compiler-rt] Fix check-builtins buildbot failures (PR #174443)

[Hans Wennborg via llvm-commits]

zmodem wrote:

We're seeing some test failures, which I'm not sure started after this or one of the previous patches, where builtins tests with "REQUIRES: crt" fail on Mac and Windows. (For example `compiler-rt/test/builtins/Unit/ctor_dtor.c`)

On Windows for example, we get errors like `error: no such file or directory: 'crt1.o'` which seems fair, given that COMPILER_RT_BUILD_CRT only builds crtbegin/end.o I think. Do you know how that's supposed to work?

The same tests also fail on Mac with similar errors.

(Our bug: https://crbug.com/474402846)

https://github.com/llvm/llvm-project/pull/174443