Merge branch 'maint'

Merge branch 'maint'

* maint:
  Bail out on option -gsplit-dwarf which produces multiple output files
  Treat zero length object files as invalid
  Fix path canonicalization in make_relative_path when path doesn't exist
  Handle some dirname() special cases as expected
  Correct make_relative_path comment

Conflicts:
	ccache.c
	compopt.c
	test/test_argument_processing.c
	test/test_util.c