Redo escaping in GN

third_party/mesa/BUILD.gn

 # Copyright 2014 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/ui.gni")
 
 config("mesa_headers_config") {
   include_dirs = [ "src/include" ]
   if (use_x11) {
     defines = [ "MESA_EGL_NO_X11_HEADERS" ]
@@ skipping 698 matching lines @@
 
   if (is_android && !is_clang) {
     # Disable sincos() optimization to avoid a linker error
     # since Android's math library doesn't have sincos().
     # Either -fno-builtin-sin or -fno-builtin-cos works.
     cflags += [ "-fno-builtin-sin" ]
   }
 
   if (is_win) {
     # Because we're building as a static library
-    defines += [ "_GLAPI_NO_EXPORTS" ]
+    defines = [ "_GLAPI_NO_EXPORTS" ]
   }
 
   deps = [
     ":mesa_headers",
     ":mesa_libglslcommon",
   ]
 }
 
 
 # Building this target will hide the native OpenGL shared library and
@@ skipping 20 matching lines @@
 #
 #  include_dirs = [ "src/src/mesa/drivers" ]
 #
 #  deps = [
 #    ":mesa_headers",
 #    ":mesa",
 #  ]
 #}
 
 # TODO(GYP) Android osmesa_in_lib_dir target.