unittest: Add `HasFatalFailure`

Implement `HasFatalFailure` function, matching the function of the same
name `googletest` provides. This allows test functions to check whether
a subroutine internally failed any asserts to react accordingly. (Most
likely to `ASSERT_EQ(false, HasFatalFailures());` so the top-level test
function exits as well.)

Bug: None
Test: build
Change-Id: Ia07b1f60007a44c6ed544207c74add26eee52876
1 file changed