Remove the use of getSubtarget in the creation of the X86

Remove the use of getSubtarget in the creation of the X86
PassManager instance. In one case we can make the determination
from the Triple, in the other (execution dependency pass) the
pass will avoid running if we don't have any code that uses that
register class so go ahead and add it to the pipeline.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228334 91177308-0d34-0410-b5e6-96231b3b80d8