[X86] Avoid clobbering ESP/RSP in the epilogue.

Summary:
In r345197 ESP and RSP were added to GR32_TC/GR64_TC, allowing them to
be used for tail calls, but this also caused `findDeadCallerSavedReg` to
think they were acceptable targets for clobbering. Filter them out.

Fixes PR40289.

Patch by Geoffry Song!

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D56617

llvm-svn: 351146