Detemplatize LOHDirective.

The ARM64 backend uses it only as a container to keep an MCLOHType and
Arguments around so give it its own little copy. The other functionality
isn't used and we had a crazy method specialization hack in place to
keep it working. Unfortunately that was incompatible with MSVC.

Also range-ify a couple of loops while at it.

llvm-svn: 205114