[lld-macho] Avoid requiring shell in tests

There are 3 remaining tests that still have `REQUIRE: shell`:
* color-diagnostics.test -- seems necessary for ANSI escape sequence support
* stabs.s -- the shell part could be removed, but I don't think we can support
  the test on Windows anyway due to its reliance on `touch` to set the modtime
* framework.s -- uses symlinks, I'm not sure this works on Windows

Addresses PR49512.

Reviewed By: #lld-macho, alexshap

Differential Revision: https://reviews.llvm.org/D98395