[test] Configure GTest for thread-safe death tests.

Most V8 unit tests are multi-threaded, so configure GTest to use the
thread-safe GTest implementation by default.

This can be overridden on a per-test basis by setting:
  testing::FLAGS_gtest_death_test_style = "fast";
during the test's SetUp() (see the GTest documentation for details).

Bug: v8:10143
Change-Id: I7414c5d8ae22eb8d9b8c4813f958ca571e1d0310
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2011085
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65873}

test/unittests/run-all-unittests.cc

@@ -38,6 +38,10 @@ int main(int argc, char** argv) {
   // Don't catch SEH exceptions and continue as the following tests might hang
   // in an broken environment on windows.
   testing::GTEST_FLAG(catch_exceptions) = false;
+
+  // Most V8 unit-tests are multi-threaded, so enable thread-safe death-tests.
+  testing::FLAGS_gtest_death_test_style = "threadsafe";
+
   testing::InitGoogleMock(&argc, argv);
   testing::AddGlobalTestEnvironment(new DefaultPlatformEnvironment);
   v8::V8::SetFlagsFromCommandLine(&argc, argv, true);