Generalize emitAbsoluteSymbolDiff.

This makes emitAbsoluteSymbolDiff always succeed and moves logic from the asm
printer to it.

The object one now also works on ELF. If two symbols are in the same fragment,
we will never move them apart.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239552 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed