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

[Nikita Popov via llvm-commits]

nikic wrote:

Trying to compare this with Linux. If I just enable the compiler-rt runtime, builtins are built for x86_64 and i386, but it looks like tests only get run for x86_64. Do I need to do something extra to run the i386 tests as well?

In the test invocations I see explicit `-m64` though, so I assume I'd see `-m32` for the i386 tests if they were running. I haven't checked where exactly we add these flags on Linux, but I'd expect the same place should be adding `--target` on Windows?

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