isl: Avoid EXPECT_DEATH in unit tests

isl: Avoid EXPECT_DEATH in unit tests

EXPECT_DEATH works by forking the process and letting the forked process
fail with an assertion. This process is evidently incredibly expensive,
taking ~30 seconds to run the whole isl_aux_info_test on a 2.8GHz
Skylake. Annoyingly all of the (expected) assertion failures also leaves
lots of messages in dmesg and potentially generates lots of coredumps.

Instead, avoid the expense of fork/exec by redefining assert() and
unreachable() in the code we're testing to return a unit-test-only
value. With this patch, the test takes ~1ms.

Also, while modifying the EXPECT_EQ() calls, reverse the arguments so
that the expected value comes first, as is intended. Otherwise gtest
failure messages don't make much sense.

Fixes: https://gitlab.freedesktop.org/mesa/mesa/issues/2567
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4174>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4174>