https://reviews.llvm.org/D69701 added support for on-the-fly argument
changes for update scripts. I recently wanted to keep some manual check
lines in a test generated by update_cc_test_checks.py in our CHERI fork, so
this commit adds support for UTC_ARGS in update_cc_test_checks.py. And since
I was refactoring the code to be in common.py, I also added it for
update_llc_test_checks.py.
Reviewed By: jdoerfert, MaskRay
Differential Revision: https://reviews.llvm.org/D78478
Having tests that depend on clang inside llvm/ are not a good idea since
it can break incremental `ninja check-llvm`.
Fixes https://llvm.org/PR44798
Reviewed By: lebedev.ri, MaskRay, rsmith
Differential Revision: https://reviews.llvm.org/D74051