Enable -Wformat and -Wformat-security by default.


--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -202,7 +202,7 @@ 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
@@ -392,7 +392,7 @@ 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/gcc.info
+++ b/gcc/doc/gcc.info
@@ -3237,6 +3237,9 @@ option was used.
      `-Wformat-nonliteral', `-Wformat-security', and `-Wformat=2' are
      available, but are not included in `-Wall'.
 
+     In Gentoo this option is enabled by default for C, C++, ObjC, ObjC++.
+     To disable, use `-Wformat=0'.
+
 `-Wformat-y2k'
      If `-Wformat' is specified, also warn about `strftime' formats
      that may yield only a two-digit year.
@@ -3279,6 +3282,11 @@ option was used.
      about, but in future warnings may be added to `-Wformat-security'
      that are not included in `-Wformat-nonliteral'.)
 
+     In Gentoo this option is enabled by default for C, C++, ObjC, ObjC++.
+     To disable, use `-Wno-format-security', or disable all format warnings
+     with `-Wformat=0'.  To make format security warnings fatal, specify
+     `-Werror=format-security'.
+
 `-Wformat=2'
      Enable `-Wformat' plus format checks not included in `-Wformat'.
      Currently equivalent to `-Wformat -Wformat-nonliteral