Small fixes for TBB on windows

Changed an #ifdef ISPC_IS_WINDOWS in the definition of TaskInfo to #ifdef ISPC_USE_CONCRT, and fixed two calls to taskCount() that were missing parentheses.
Merge pull request #801 from ifilippov/master

support LLVM trunk
Merge pull request #799 from motiz88/patch-1

Small fixes for TBB on Windows
changing +/-feature regulation to CPU regulation
Merge pull request #802 from ifilippov/avx2

Changing +/-feature regulation to CPU regulation
support LLVM build