[test] Fix auto-detect cfi

TBR=sergiyb@chromium.org
NOTRY=true

Bug: v8:6917
Change-Id: Ia417ab5cf59a6c2894de67d5519394629b6ab1b9
Reviewed-on: https://chromium-review.googlesource.com/727936Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48735}

tools/testrunner/base_runner.py

@@ -312,6 +312,7 @@ class BaseTestRunner(object):
     # trying to use inconsistent options.
     for param, value in (
       ('asan', build_config["is_asan"]),
+      ('cfi_vptr', build_config["is_cfi"]),
       ('dcheck_always_on', build_config["dcheck_always_on"]),
       ('gcov_coverage', build_config["is_gcov_coverage"]),
       ('msan', build_config["is_msan"]),