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/getargs.c

@@ -218,6 +218,7 @@ static const char * const warnings_args[] =
   "yacc            - incompatibilities with POSIX Yacc",
   "conflicts-sr    - S/R conflicts",
   "conflicts-rr    - R/R conflicts",
+  "deprecated      - obsolete constructs",
   "other           - all other warnings",
   "all             - all of the above",
   "error           - warnings are errors",
@@ -231,6 +232,7 @@ static const int warnings_types[] =
   Wyacc,
   Wconflicts_sr,
   Wconflicts_rr,
+  Wdeprecated,
   Wother,
   Wall,
   Werror