[tools] Enable vpointer-sanitation on UBSan bots

Even though we override chromiums UBSan settings in our own BUILD.gn to
include all sanitizers, vptr is still excluded. The reason is that
the vptr sanitizer requires RTTI to be enabled.

The "is_ubsan_vptr" flag will enable RTTI as well as some linker flags
to export libc++abi symbols. Both are required by the vptr sanitizer.

Change-Id: I803ed71781bb3edc824bbe5d1aaa830841b4b304
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1566511Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60841}

infra/mb/mb_config.pyl

@@ -759,13 +759,13 @@
       # TODO(krasin): Remove is_ubsan_no_recover=true when
       # https://llvm.org/bugs/show_bug.cgi?id=25569 is fixed and just use
       # ubsan instead.
-      'gn_args': 'is_ubsan=true is_ubsan_no_recover=true',
+      'gn_args': 'is_ubsan=true is_ubsan_no_recover=true is_ubsan_vptr=true',
     },
 
     'ubsan_recover': {
       'mixins': ['v8_enable_test_features'],
       # Ubsan with recovery.
-      'gn_args': 'is_ubsan=true is_ubsan_no_recover=false',
+      'gn_args': 'is_ubsan=true is_ubsan_no_recover=false is_ubsan_vptr=true',
     },
 
     'v8_check_header_includes': {