- causes warnings about unused -I options, because they are preprocessing options
  and Clang complains that they are unused in pure compilation
- Clang supresses some warnings from expansions of macros in system headers, but those
  would be already expanded and thus warned about
- Clang prints relevant source lines with errors/warnings in them and would show
  them preprocessed (this should actually apply to GCC4.8+ too)

Change-Id: I02c86c43a657d078e347e4ecd5c1e2ff07db2886