c-decl.c (store_parm_decls_oldstyle): Let diagnostic machinery decide if the warning will be printed.

* c-decl.c (store_parm_decls_oldstyle): Let diagnostic machinery
decide if the warning will be printed.
* calls.c (expand_call): Likewise.
* function.c (init-function_start): Likewise.

* common.opt (-fdiagnostics-show-option): New.
* opts.c (option_enabled): Accept the option index instead of a
pointer to the option descriptor.
* opts.h (option_enabled): Likewise.
* toplev.c (print_switch_values): Pass option index, not option
descriptor.
* diagnostic.h (diagnostic_info): Add option_index.
* diagnostic.c: Include opts.h.
(diagnostic_set_info): Initialize option_index.
(diagnostic_report_diagnostic): Amend option name if appropriate.
(warning): Check to see if the specified warning is enabled.
Store option index.
* doc/invoke.texi (-fdiagnostics-show-options): Document.

From-SVN: r99169