Fix repeated "-Wunknown-pragmas -Wno-error=unknown-pragmas".

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/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 1673 matching lines @@
 }
 
 # No symbols.
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
     asmflags = cflags
   }
 }
 
+# On Linux and Android, the "grit" template wants to disable the warning about
+# unknown pragmas. However since gn does not deduplicate the flags from configs
+# but only the config themselves, if the template declares a "config" for that
+# purpose, the flag will end up being repeated for each dependent "grit" target.
+# Using a separate config solves this problem.
+config("disable_unknown_pragma") {
+  if (is_clang) {
+    cflags = [
+      "-Wunknown-pragmas",
+      "-Wno-error=unknown-pragmas",
+    ]
+  }
+}
+
 # Default symbols.
 config("default_symbols") {
   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)
   }
 }
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }