Fix UBSAN VPTR build breakage due to unused sanitizer coverage argument.

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 62 matching lines @@
         'cflags': [
           '-fPIC',
         ],
       }],
       ['ubsan_vptr == 1', {
         'cflags!': [
           # UBsan's vptr is not compatible with -fno-rtti,
           # which is used by gallium/auxiliary/Makefile.
           '-fsanitize=null',
           '-fsanitize=vptr',
+          '-fsanitize-coverage=<(sanitizer_coverage)',
         ],
       }],
     ],
   },
   'targets': [
     {
       'target_name': 'mesa_headers',
       'type': 'none',
       'direct_dependent_settings': {
         'include_dirs': [
@@ skipping 647 matching lines @@
                 '<(PRODUCT_DIR)/libosmesa.so',
                 '<(SHARED_LIB_DIR)/libosmesa.so',
               ],
             },
           ],
         },
       ],
     }],
   ],
 }