Lower severity of 3 tidy warnings

* bcmp/bcopy/bzero are not insecureAPI on Android.
* Android projects may enable/disable clang-tidy checks locally;
  warn/*patterns.py keep global classification of all warnings.

Test: warn.py --url=http://cs/android --separator='?l=' build.log > warnings.html
Test: warn.py --gencsv build.log > warnings.csv
Change-Id: I7720f7babd0a33c1b6602c9a8bb67565c45db94e