Enable -Wformat and -Wformat-security by default.

--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -696,7 +696,7 @@ Warn about function calls with format strings that write past the end
 of the destination region.  Same as -Wformat-overflow=1.
 
 Wformat-security
-C ObjC C++ ObjC++ Var(warn_format_security) Warning LangEnabledBy(C ObjC C++ ObjC++,Wformat=, warn_format >= 2, 0)
+C ObjC C++ ObjC++ Var(warn_format_security) Init(1) Warning LangEnabledBy(C ObjC C++ ObjC++,Wformat=, warn_format >= 2, 0)
 Warn about possible security problems with format functions.
 
 Wformat-signedness
@@ -717,7 +717,7 @@ C ObjC C++ ObjC++ Var(warn_format_zero_length) Warning LangEnabledBy(C ObjC C++
 Warn about zero-length formats.
 
 Wformat=
-C ObjC C++ ObjC++ Joined RejectNegative UInteger Var(warn_format) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall, 1, 0) IntegerRange(0, 2)
+C ObjC C++ ObjC++ Joined RejectNegative UInteger Var(warn_format) Init(1) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall, 1, 0) IntegerRange(0, 2)
 Warn about printf/scanf/strftime/strfmon format string anomalies.
 
 Wformat-overflow=