third_party/mesa: turn off ubsan_vptr, since it's compiled without rtti.

build/config/BUILDCONFIG.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.
 
 # =============================================================================
 # PLATFORM SELECTION
 # =============================================================================
 #
 # There are two main things to set: "os" and "cpu". The "toolchain" is the name
 # of the GN thing that encodes combinations of these things.
@@ skipping 440 matching lines @@
   "//build/config/compiler:compiler",
   "//build/config/compiler:clang_stackrealign",
   "//build/config/compiler:compiler_arm_fpu",
   "//build/config/compiler:chromium_code",
   "//build/config/compiler:default_include_dirs",
   "//build/config/compiler:default_optimization",
   "//build/config/compiler:default_symbols",
   "//build/config/compiler:no_rtti",
   "//build/config/compiler:runtime_library",
   "//build/config/sanitizers:default_sanitizer_flags",
+  "//build/config/sanitizers:ubsan_vptr_flags",
   "//build/config/sanitizers:default_sanitizer_coverage_flags",
 ]
 if (is_win) {
   _native_compiler_configs += [
     "//build/config/win:lean_and_mean",
     "//build/config/win:nominmax",
     "//build/config/win:unicode",
     "//build/config/win:winver",
     "//build/config/win:vs_code_analysis",
   ]
@@ skipping 150 matching lines @@
     forward_variables_from(invoker, "*", [ "visibility" ])
 
     # All shared libraries must have the sanitizer deps to properly link in
     # asan mode (this target will be empty in other cases).
     if (!defined(deps)) {
       deps = []
     }
     deps += [ "//build/config/sanitizers:deps" ]
   }
 }