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: #2567 (closed)