Merge pull request #906 from ncos/ispc_build_fails

fixed ISPC compilation fail caused by LLVM DIBuilder API change
Tracking LLVM trunk: SmallPtrSet changes
Merge pull request #908 from dbabokin/trunk

Tracking LLVM trunk: SmallPtrSet changes
Fix for DWARF debug info generation pipeline

Applies to LLVM-3.4, -3.5 and -trunk builds of ISPC
Build fix for LLVM trunk - changed include structure
Merge pull request #910 from dbabokin/trunk

Build fix for LLVM trunk - changed include structure
Merge pull request #911 from aguskov/master

Fix for DWARF debug info generation pipeline