[gdb] Add missing i18n support to error strings (part 2)

Add missing i18n support to some error strings.

Result of:
...
$ find gdb* -type f -name "*.[ch]" -o -name "*.cc" \
    | egrep -v /testsuite/ \
    | xargs sed -i \
        '/"[ \t]*%s[ \t]*"/b l;s/\([ \t]\)error (\("[^"]*"\),$/\1error (_(\2),/;:l'
...

Approved-By: Tom Tromey <tom@tromey.com>