Don't enable the post-RA scheduler on x86 except at -O3. In its

Don't enable the post-RA scheduler on x86 except at -O3. In its
current form, it is too expensive in compile time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90781 91177308-0d34-0410-b5e6-96231b3b80d8