R_X86_64_NONE can be emitted without a symbol associated (well,
in theory it should never be emitted in an ABI-compliant relocatable
object). So, if there's no symbol associated to a reloc, emit one
with an empty name, instead of crashing.
Ack'ed by Michael Spencer offline.
PR: 31768
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293224 91177308-0d34-0410-b5e6-96231b3b80d8