Fix PR7054 - Assertion `Symbol->isUndefined() && "Cannot define a symbol twice!"' failed.

Users can write broken code that emits the same label twice with asm renaming,
detect this and emit a fatal backend error instead of aborting.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103140 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed