Enable -Wformat in linux, android, chromeos, cast builds.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/ccache.gni")
 
@@ skipping 945 matching lines @@
 
   if (is_clang) {
     cflags += [
       # Lots of third-party libraries have unused variables. Instead of
       # suppressing them individually, we just blanket suppress them here.
       "-Wno-unused-variable",
     ]
   }
 
   if (is_linux || is_android) {
-    cflags += [
-      # Don't warn about printf format problems. This is off by default in gcc
-      # but on in Ubuntu's gcc(!).
-      "-Wno-format",
-    ]
     cflags_cc += [
       # Don't warn about hash_map in third-party code.
       "-Wno-deprecated",
     ]
   }
 
   configs = [ ":default_warnings" ]
 }
 
 # rtti ------------------------------------------------------------------------
@@ skipping 326 matching lines @@
   if (symbol_level == 0) {
     configs = [ ":no_symbols" ]
   } else if (symbol_level == 1) {
     configs = [ ":minimal_symbols" ]
   } else if (symbol_level == 2) {
     configs = [ ":symbols" ]
   } else {
     assert(false)
   }
 }