diagnostics: factor the list of warning names

* src/getargs.h, src/getargs.c (warnings_args, warnings_types): Make
them public.
* src/complain.h, src/complain.c (warnings_print_categories): Its
only use outside complain.c was removed in a recent commit, so
make it static.
Simplify its implementation.
Use warnings_args and warnings_types.
* src/muscle-tab.c (muscle_percent_define_check_values): Make it
silent.

src/complain.h

@@ -57,9 +57,6 @@ extern warnings warnings_flag;
 /** What warnings are made errors.  */
 extern warnings errors_flag;
 
-/** Display a "[-Wyacc]" like message on stderr.  */
-void warnings_print_categories (warnings warn_flags);
-
 /** Make a complaint, with maybe a location.  */
 void complain (location const *loc, warnings flags, char const *message, ...)
   __attribute__ ((__format__ (__printf__, 3, 4)));