Fix errors generated by knc.h present in icpc 13.1 

- Changed implementation of '__scatter64_i64' for icpc 13.1 to suit it's set of intrinsics
- Silenced warnings produced by 'reduce...' functions on icpc 13.1
- Update fail_db.txt with passes fails for icpc 15.0 and 13.1

NOTE, there is one new runfail: ./tests/pmuls_vi64.ispc -O2