stack guard - use __builtin_frame_address(0)

Pointers on the stack are pretty whack.
But clang builtins, they got yo' back.

Fixes: 258970199 (: or it'll get re-filed :)
Test: libbinderthreadstateutils_test

Change-Id: I4a7af39c680562a1b7a7c2c71c54eb371d857d5e
1 file changed