tests/test-driver Miscelaneous improvements.

Some times the test can be aborted for reasons others than failed assertions, such as segmentation faults or reaching unreacheable code.

To speed up noticing these problems, the [SIGABRT] and [SIGSEGV] tags are printed on the corresponding exit codes.

Also, "reached unreachable code" lines are also detected and printed with an [AF] tag.

An error may look like this:

FAIL: tests/hlsl/some-test.shader_test
    (SM4.0-SM5.1)OpenGL/SPIR-V 43[XF] 79[XF] 126[XF] 149[XF] 159[XF]
    [AF] vkd3d/libs/vkd3d-shader/hlsl.c:246: Aborting, reached unreachable code.
    [SIGABRT] Aborted (core dumped)