Harden CrasherTest::Trap under sanitizers.

The use of __builtin_abort in CrasherTest::Trap breaks with
-ftrap-function=abort, because then the argument of Trap is no longer in
the first argument register at the time of crash.

This flag is added when *any* sanitizer is enabled on the target, even harmless
ones like memtag-heap. See sanitize.go:769.

Fix CrasherTest::Trap to be a little more reliable.

Test: debuggerd_test with SANITIZE_TARGET=memtag_heap
Change-Id: I150f1c0355bd6f2bfabfa5a7bba125acdde1120e