clang/win: Build chromium code without -Wno-incompatible-pointer-types.

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 626 matching lines @@
   cflags = []
 
   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 = [
+      # Because we're building as a static library
+      "_GLAPI_NO_EXPORTS",
+
+      # Generated files use const only if __cplusplus or __STDC__ is defined.
+      # On Windows, neither is defined, so define YY_USE_CONST to explicitly
+      # enable const.
+      "YY_USE_CONST",
+    ]
   }
 
   deps = [
     ":mesa_headers",
   ]
 }
 
 if (!is_android) {  # TODO(GYP) enable for Android.
   # Building this target will hide the native OpenGL shared library and
   # replace it with a slow software renderer.
@@ skipping 44 matching lines @@
         "KEYWORD2=GLAPIENTRY",
       ]
     }
   }
 } else {
   #  Placeholder to allow targets to unconditionally depend on this.
   group("osmesa") {
   }
 }  # !is_android
 # TODO(GYP) Android osmesa_in_lib_dir target.