message: Workaround for the problem that clang header contains typename with name CALLBACK
diff: #include <stdio.h>
  #include <sys/stat.h>
  #include <sys/types.h>
  -#ifdef ISPC_HOST_IS_WINDOWS
  -#include <io.h>
  -#include <windows.h>
  -#endif
  #include <clang/Basic/TargetInfo.h>
  #include <clang/Frontend/CompilerInstance.h>
  #endif
  #ifdef ISPC_HOST_IS_WINDOWS
  +#include <io.h>
  +// windows.h defines CALLBACK as __stdcall
  +// clang/Analysis/CFG.h contains typename with name CALLBACK, which is got screwed up.
  +// So we include it after clang includes.
  +#include <windows.h>
  // Note that this define must be after clang includes, as they undefining this symbol.
  #define strcasecmp stricmp
  #endif
  