Re-commit r265039 "[X86] Merge adjacent stack adjustments in...

Re-commit r265039 "[X86] Merge adjacent stack adjustments in eliminateCallFramePseudoInstr (PR27140)"

Third time's the charm? The previous attempt (r265345) caused ASan test
failures on X86, as broken CFI caused stack traces to not work.

This version of the patch makes sure not to merge with stack adjustments
that have CFI, and to not add merged instructions' offests to the CFI
about to be generated.

This is already covered by the lit tests; I just got the expectations
wrong previously.

llvm-svn: 265623