> All in all, I think a better solution would be to put that information
> directly in the language_defn itself, via a new "attribute".
> Something like a...

I ended up choosing this approach. lookup names is still a bit
foggy for me, so the comments I wrote and/or the name of the
new language_defn attribute might be a bit off. As always, I am
grateful for suggestions :).

gdb/ChangeLog:

        PR gdb/22670
        * dwarf2read.c (dwarf2_physname): Do not return the demangled
        symbol name is the CU's language stores symbol names in linkage
        format.
        * language.h (struct language_defn)
        <la_store_sym_names_in_linkage_form_p>: New field.  Adjust
        all instances of this struct.

gdb/testsuite/ChangeLog:

        * gdb.ada/maint_with_ada.exp: Remove PR gdb/22670 setup_kfail.

        * gdb.ada/notcplusplus: New testcase.

        * gdb.base/c-linkage-name.c: New file.
        * gdb.base/c-linkage-name.exp: New testcase.

Tested on x86_64-linux.
This also passes AdaCore's internal GDB testsuite.

OK to commit?

Thank you!
-- 
Joel