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

(fixed unit tests by making comparisons stable)

This reverts commit 1b2d359ce256fd6737da4e93833346a0bd6d7583.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315056 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed