llvm-mc: When handling a .set, make sure to print subsequent references to the

llvm-mc: When handling a .set, make sure to print subsequent references to the
symbol as the symbol name itself, not the expression it was defined to. These
have different semantics due to the quirky .set behavior (which absolutizes an
expression that would otherwise be treated as a relocation).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79025 91177308-0d34-0410-b5e6-96231b3b80d8