[Utils][X86] Help update_llc_test_checks.py to recognise retl/retq to reduce...

[Utils][X86] Help update_llc_test_checks.py to recognise retl/retq to reduce CHECK duplication (PR35003)

This patch replaces the --x86_extra_scrub command line argument to automatically support a second level of regex-scrubbing if it improves the matching of nearly-identical code patterns. The argument '--extra_scrub' is there now to force extra matching if required.

This is mostly useful to help us share 32-bit/64-bit x86 vector tests which only differs by retl/retq instructions, but any scrubber can now technically support this, meaning test checks don't have to be needlessly obfuscated.

I've updated some of the existing checks that had been manually run with --x86_extra_scrub, to demonstrate the extra "ret{{[l|q]}}" scrub now only happens when useful, and re-run the sse42-intrinsics file to show extra matches - most sse/avx intrinsics files should be able to now share 32/64 checks.

Tested with the opt/analysis scripts as well which share common code - AFAICT the other update scripts use their own versions.

Differential Revision: https://reviews.llvm.org/D47485

llvm-svn: 333749