[mach-o] refactor KindHandler into ArchHandler and simplify passes.

All architecture specific handling is now done in the appropriate
ArchHandler subclass.

The StubsPass and GOTPass have been simplified.  All architecture specific
variations in stubs are now encoded in a table which is vended by the
current ArchHandler.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@213187 91177308-0d34-0410-b5e6-96231b3b80d8