[llvm] [update_mc_test_checks] Fix llvm-mc invocation on Windows by avoiding echo pipe (PR #179381)

[Brox Chen via llvm-commits]

broxigarchen wrote:

> Right now we mark the `update_mc_test_checks.py` tests as unsupported on Windows:
> 
> https://github.com/llvm/llvm-project/blob/114f3b530bae5a195234e3bd1c1328b38b39a000/llvm/test/tools/UpdateTestChecks/update_mc_test_checks/lit.local.cfg#L4
> 
> With this change, do all of those tests start passing?

Hi @boomanaiden154 The script is originally wrotten for linux. I remembered I caught some issues in windows CI at that time thus the it was skipped. It seems this patch is trying to fix some issues for windows platform so I think this is moving in a good direction.

@harrisonGPU can you also try to remove the windows check in "[llvm-project/llvm/test/tools/UpdateTestChecks/update_mc_test_checks/lit.local.cfg](https://github.com/llvm/llvm-project/blob/114f3b530bae5a195234e3bd1c1328b38b39a000/llvm/test/tools/UpdateTestChecks/update_mc_test_checks/lit.local.cfg#L4)" and see if the windows CI pass?

Even if it does not pass, I believe we can still move forward with it


https://github.com/llvm/llvm-project/pull/179381