[MergeICmps] Disable mergeicmps if the target does not want to handle memcmp expansion.

Summary: This is to avoid e.g. merging two cheap icmps if the target is not going to expand to something nice later.

Reviewers: dberlin, spatel

Subscribers: davide, nemanjai

Differential Revision: https://reviews.llvm.org/D38232

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314970 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed