Remove "Rewrite Symbols" from codegen pipeline

It breaks up the function pass manager in the codegen pipeline.

With empty parameters, it looks at the -mllvm flag -rewrite-map-file.
This is likely not in use.

Add a check that we only have one function pass manager in the codegen
pipeline.

Some tests relied on the fact that we had a module pass somewhere in the
codegen pipeline.

addr-label.ll crashes on ARM due to this change. This is because a
ARMConstantPoolConstant containing a BasicBlock to represent a
blockaddress may hold an invalid pointer to a BasicBlock if the
blockaddress is invalidated by its BasicBlock getting removed. In that
case all referencing blockaddresses are RAUW a constant int. Making
ARMConstantPoolConstant::CVal a WeakVH fixes the crash, but I'm not sure
that's the right fix. As a workaround, create a barrier right before
ISel so that IR optimizations can't happen while a
ARMConstantPoolConstant has been created.

Reviewed By: rnk, MaskRay, compnerd

Differential Revision: https://reviews.llvm.org/D99707