Enable -Wformat and -Wformat-security by default.


--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -201,7 +201,7 @@ int warn_unknown_pragmas; /* Tri state variable.  */
 /* Warn about format/argument anomalies in calls to formatted I/O functions
    (*printf, *scanf, strftime, strfmon, etc.).  */
 
-int warn_format;
+int warn_format = 1;
 
 /* C/ObjC language option variables.  */
 
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -384,7 +384,7 @@ C ObjC C++ ObjC++ Var(warn_format_contains_nul) Warning
 Warn about format strings that contain NUL bytes
 
 Wformat-security
-C ObjC C++ ObjC++ Var(warn_format_security) Warning
+C ObjC C++ ObjC++ Var(warn_format_security) Init(1) Warning
 Warn about possible security problems with format functions
 
 Wformat-y2k
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -3111,6 +3111,9 @@ aspects of format checking, the options @option{-Wformat-y2k},
 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
 
+In Gentoo this option is enabled by default for C, C++, ObjC, ObjC++.
+To disable, use @option{-Wformat=0}.
+
 @item -Wformat-y2k
 @opindex Wformat-y2k
 @opindex Wno-format-y2k
@@ -3164,6 +3167,11 @@ currently a subset of what @option{-Wformat-nonliteral} warns about, but
 in future warnings may be added to @option{-Wformat-security} that are not
 included in @option{-Wformat-nonliteral}.)
 
+In Gentoo this option is enabled by default for C, C++, ObjC, ObjC++.
+To disable, use @option{-Wno-format-security}, or disable all format warnings
+with @option{-Wformat=0}.  To make format security warnings fatal, specify
+@option{-Werror=format-security}.
+
 @item -Wformat=2
 @opindex Wformat=2
 @opindex Wno-format=2