Reset some of the target options which affect code generation.

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