added LLVM_3_6 var
fixed 3.6 llvm build in type.cpp
removed duplicatees in Makefile
checked Makefile 'if' constructions, fixed ReleaseNotes.txt, added comments to util.m4
rewritten comment for util.m4
Merge pull request #828 from ncos/ispc_build_fails

Add support for LLVM 3.6 build