[AsmParser] Diagnose empty symbol for .set directive

Summary: Diagnose empty symbol to avoid hitting assertion in MCContext::getOrCreateSymbol

Reviewers: eli.friedman, rengolin

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D26728

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@288390 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed