* c-common.c (warn_format_security): New variable.
(check_format_info): Warn about non-literal formats with no format
arguments if either -Wformat-nonliteral or -Wformat-security is
specified.
(set_Wformat): Set warn_format_security for settings other than 1.
* c-common.h (warn_format_security): Declare.
* c-decl.c (c_decode_option): Decode -Wformat-security and
-Wno-format-security.
* invoke.texi: Document -Wformat-security.
* toplev.c (documented_lang_options): Include -Wformat-security
and -Wno-format-security.