Add osmesa to GN build.

third_party/mesa/mesa.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'generated_src_dir': 'src/chromium_gensrc',
   },
   'target_defaults': {
     'defines': [
@@ skipping 205 matching lines @@
         'src/src/glsl/opt_noop_swizzle.cpp',
         'src/src/glsl/opt_redundant_jumps.cpp',
         'src/src/glsl/opt_structure_splitting.cpp',
         'src/src/glsl/opt_swizzle_swizzle.cpp',
         'src/src/glsl/opt_tree_grafting.cpp',
         'src/src/glsl/program.h',
         'src/src/glsl/ralloc.c',
         'src/src/glsl/ralloc.h',
         'src/src/glsl/s_expression.cpp',
         'src/src/glsl/s_expression.h',
-        'src/src/glsl/standalone_scaffolding.cpp',
-        'src/src/glsl/standalone_scaffolding.h',
+        # This file is not needed and has duplicate symbols (although it
+        # happens to link because of static library link ordering).
+        #'src/src/glsl/standalone_scaffolding.cpp',
+        #'src/src/glsl/standalone_scaffolding.h',
         'src/src/glsl/strtod.c',
         'src/src/glsl/strtod.h',
       ],
       'conditions': [
         ['clang == 1', {
           'xcode_settings': {
             'WARNING_CFLAGS': [
               '-Wno-tautological-constant-out-of-range-compare',
             ],
             'WARNING_CFLAGS!': [
@@ skipping 592 matching lines @@
                 '<(PRODUCT_DIR)/libosmesa.so',
                 '<(SHARED_LIB_DIR)/libosmesa.so',
               ],
             },
           ],
         },
       ],
     }],
   ],
 }