[scudo] Make death tests use SCUDO_XXX_DEATH_TEST. (#206196)
On Android, we want to disable the tombstone generation on expected
crashes to speed up running the tests. Also, this means that any
tombstone files will be real crashes and it's not necessary to search
for the right tombstone if one of the tests crashes unexpectedly.
In order to do the above, add SCUDO_EXPECT_DEATH_TEST and
SCUDO_ASSERT_DEATH_TEST that will disable tombstoned on Android but do
nothing on all other platforms.