Fix the stack protector death test.

Now __stack_chk_fail calls abort(3) directly, we terminate with
SIGSEGV rather than SIGABRT. (Because of the workaround for the
debuggerd lossage in the abort(3) implementation, which was the
motivation for switching __stack_chk_fail over to abort(3).)

Also clarify the comment on the weird pthread death test, so it
doesn't get copied and pasted onto real death tests.

Change-Id: Ie832eaded61359c99e7a10db65e28f35e8f63eed
diff --git a/tests/stack_protector_test.cpp b/tests/stack_protector_test.cpp
index 97d5ad6..7946bbc 100644
--- a/tests/stack_protector_test.cpp
+++ b/tests/stack_protector_test.cpp
@@ -117,11 +117,9 @@
   __stack_chk_guard = 0x12345678;
 }
 
-// We have to say "DeathTest" here so gtest knows to run this test (which exits)
-// in its own process.
 TEST(stack_protector_DeathTest, modify_stack_protector) {
   ::testing::FLAGS_gtest_death_test_style = "threadsafe";
-  ASSERT_EXIT(do_modify_stack_chk_guard(), testing::KilledBySignal(SIGABRT), "");
+  ASSERT_EXIT(do_modify_stack_chk_guard(), testing::KilledBySignal(SIGSEGV), "");
 }
 
 #endif