[MC] Make symbol version errors non-fatal

We stil don't have a source location, which is pretty lame, but at least
we won't tell the user to file a clang bug report anymore.

Fixes PR40712

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353907 91177308-0d34-0410-b5e6-96231b3b80d8