[x86][slh] Move isDataInvariant* functions
Patch by Zola Bridges!
From the review:
I moved these functions to X86InstrInfo.cpp, so they are available from
another pass. In addition, this is a step toward resolving the FIXME to
move this metadata to the instruction tables.
This is the final step to make these two data invariance checks
available for non-SLH passes.
The other two steps were here:
Tested via llvm-lit llvm/test/CodeGen/X86/speculative-load-hardening*
Differential Revision: https://reviews.llvm.org/D75654