[sanitizer_common] Log a backtrace for unexpected format printf specifiers (#222658)

Occasionally I find these warning messages in ASan logs, and it is not
always easy to track down their source. This patch logs a backtrace
along with the warning message in order to make them easier to locate.

rdar://34028569

NOKEYCHECK=True
GitOrigin-RevId: 825a07ee6a6af50715d0e8c2a91cf8b74a5a12cd