adding --extra option and correction pathes to ispc compiler
Merge pull request #623 from ifilippov/testing

adding --extra option and correction pathes to ispc compiler
patch for LLVM for fails at avx-x2
Merge pull request #624 from ifilippov/fix1

patch for LLVM for fails on avx-x2 target
fix for ISPC for compfails at sse4-i8 and sse4-i16
Merge pull request #626 from ifilippov/fix1

fix for ISPC for compfails at sse4-i8 and sse4-i16