Revert "r214832 - MachineCombiner Pass for selecting faster instruction"

It broke compiling of most Benchmark and internal test, as clang got
clashed by segmentation fault or assertion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214845 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed