ANGLE's ASSERT macro was often not printing the error message before
crashing. The printing happens in the destructor of a temporary object,
but the temporary object is not guaranteed to be destroyed before ASSERT
calls __builtin_trap(). This change fixes it by introducing a new FATAL
log severity that moves the __builtin_trap() call into the destructor
after the message is printed.

Bug: 780507, angleproject:2215
Change-Id: Ica91e00d67cc95d7b59c3d59e6925ac3a93c19c5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1521839
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>