libcutils: cleanups for -fsanitize=integer

Hash functions rely on overflow behavior, so whitelist them.

ATRACE_TAG_NOT_READY: use an unsigned constant when shifting bits.
Otherwise, the value overflows on shift. The users of this constant
assign it to a uint64_t variable.

Change-Id: I21c437ce2083525e906c3ead3259ec34a1ef4b66