[compiler-rt] Fix: windows i386 builtins tests (PR #179062)

[Hans Wennborg via llvm-commits]

zmodem wrote:

Thanks for working on this!

> Without an explicit target, the tests defaulted to x64 on 64-bit Windows hosts, causing architecture mismatches and linker errors.

Technically, Clang will default to `LLVM_DEFAULT_TARGET_TRIPLE` I think. So it seems possible to have the reverse situation as well: Clang could be targeting i386 by default, and fail the builtins tests for x64.

> What is special about Windows i386 that requires this handling?

I think this is what we need to figure out. How is the target generally set when running these tests? Wouldn't we have the same problem when building builtins for 32-bit x86 on x84_64 linux for example?

https://github.com/llvm/llvm-project/pull/179062