[UpdateTestChecks] Add update_analyze_test_checks.py for cost model analysis generation

The script allows the auto-generation of checks for cost model tests to speed up their creation and help improve coverage, which will help a lot with PR36550.

If the need arises we can add support for other analyze passes as well, but the cost models was the one I needed to get done - at the moment it just warns that any other analysis mode is unsupported.

I've regenerated a couple of x86 test files to show the effect.

Differential Revision: https://reviews.llvm.org/D45272

llvm-svn: 329390