- Thanks to Kirill "tcc -b itself" should work now
  (was removed in d5f4df09)

Also:

- tests/Makefile:
  - fix spurious --I from 767410b8
  - lookup boundtest.c via VPATH (for out-of-tree build)
  - test[123]b?: fail on diff error
  - Windows: test3 now works (from e31579b0)
  - abitest: a libtcc.a made by gcc is not usable for tcc
    on WIndows - using source instead (libtcc.c)

- tccpe:
  - avoid gcc warning (x86_64)