[gdb/symtab] Emit malformed macro definition complaint once

[gdb/symtab] Emit malformed macro definition complaint once

Add a test-case gdb.dwarf2/macro-complaints.exp, that checks complaints for the
.debug_macro section.

For one malformed macro definition, I get two identical complaints:
...
During symbol reading: macro debug info contains a malformed macro definition:^M
`M1_11_MALFORMED(ARG'^M
During symbol reading: macro debug info contains a malformed macro definition:^M
`M1_11_MALFORMED(ARG'^M
...

Fix this by bailing out after the first one.

Tested on aarch64-linux.

Reviewed-By: Alexandra Petlanova Hajkova <ahajkova@redhat.com>