message: Fixed ispc build on Windows with LLVM_7.0
diff: #include <windows.h>
  #include <direct.h>
  #define strcasecmp stricmp
  + #if ISPC_LLVM_VERSION >= ISPC_LLVM_7_0
  + #include <intrin.h>
  + #endif
  #else
  #include <sys/types.h>
  #include <unistd.h>
  