[GlobalIsel] Add llvm.invariant.start and llvm.invariant.end

Port over the implementation in SelectionDAGBuilder.cpp into the IRTranslator
and update the arm64-irtranslator test.

These were causing fallbacks in CTMark/Bullet (-Rpass-missed=gisel-select),
and this patch fixes that.

https://reviews.llvm.org/D52945

llvm-svn: 343885