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

third_party/mesa/BUILD.gn

Index: third_party/mesa/BUILD.gn
diff --git a/third_party/mesa/BUILD.gn b/third_party/mesa/BUILD.gn
index 427d4b62c42471cb9a820ef717f77e2c886034bd..5996ee0a0197b0cb6e1d6b31e6dd0e0c653ea07d 100644
--- a/third_party/mesa/BUILD.gn
+++ b/third_party/mesa/BUILD.gn
@@ -127,6 +127,11 @@ config("mesa_internal_warnings") {
       "-Wno-unused-local-typedef",
     ]
   }
+  if (is_ubsan_vptr) {
+    # UBsan's vptr is not compatible with -fno-rtti,
+    # which is used by gallium/auxiliary/Makefile.
+    cflags += [ "-fno-sanitize=vptr" ]

[Dirk Pranke, 2016/04/22 23:04:56]

This is dangerous, because this is likely sensitive tot he order in which the
flags appear on the command line.

The right way to do this is to define a config that sets this flag, have that
config get included when is_ubsan_vptr is set to true, and then *remove* that
config from this target if need be (so you need to mess with the settings in
//build/config/sanitzers/BUILD.gn a bit).

+  }
   if (is_win) {
     # TODO(scottmg): http://crbug.com/143877 These should be removed if
     # Mesa is ever rolled and the warnings are fixed.