Reset some of the target options which affect code generation.

This doesn't reset all of the target options within the TargetOptions
object. This is because some of those are ABI-specific and must be determined if
it's okay to change those on the fly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176986 91177308-0d34-0410-b5e6-96231b3b80d8