[libcxx-commits] [libcxx] [libc++] Add a utility for checking the output of commands (PR #65917)

[Louis Dionne via libcxx-commits]

ldionne wrote:

Since using the real `FileCheck` still has not happened and there are many use cases for this patch, I think it would be reasonable to pursue this again. @philnik777 If you want to rebase this patch on top of `main`, I'll be happy to review it (likely when I get back from the holidays).

https://github.com/llvm/llvm-project/pull/65917