This patch is motivated by
https://github.com/llvm/llvm-project/pull/149827, where we plan on using
mangled names on structor declarations to find the exact structor
definition that LLDB's expression evaluator should call.
So far LLVM expects the declaration and definition linkage names to be
identical (or the declaration to just not have a linkage name). But we
plan on attaching the GCC-style "unified" mangled name to declarations,
which will be different to linkage name on the definition. This patch
relaxes this restriction.
c6286b30bd