[x86] Clean up some tests to use FileCheck and combine two into a single
file.

Changing code that is covered by these tests is just too hard to debug
currently, and now it will be clear the nature of the changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216643 91177308-0d34-0410-b5e6-96231b3b80d8