introduce -Wdeprecated

GCC seems to be using "deprecated" consistently over "obsoleted", so
use -Wdeprecated rather than -Wobsolete.

* src/complain.h (warnings): Add Wdeprecated.
* src/complain.c (warnings_print_categories): Adjust.
* src/getargs.c: Likewise.
* doc/bison.texi: Document it.

* src/scan-code.l: Use this category for the trailing ';' support.
* tests/actions.at: Adjust expected output.

src/complain.c

@@ -29,7 +29,8 @@
 #include "files.h"
 #include "getargs.h"
 
-warnings warnings_flag = Wconflicts_sr | Wconflicts_rr | Wother;
+warnings warnings_flag =
+  Wconflicts_sr | Wconflicts_rr | Wdeprecated  | Wother;
 
 bool complaint_issued;
 static unsigned *indent_ptr = 0;
@@ -45,6 +46,7 @@ warnings_print_categories (warnings warn_flags)
           "yacc",
           "conflicts-sr",
           "conflicts-rr",
+          "deprecated",
           "other"
         };