[ELF] - Test we are able to assign version to symbols that are not "_Z*"

This is to test the following line of the code:
https://github.com/llvm-mirror/lld/blob/master/ELF/SymbolTable.cpp#L681

If symbol does not start from _Z prefix and we have extern "C++",
we do not call demangler and use its name as is.

llvm-svn: 336353