re PR pch/13675 (#including a precompiled header more than once in the same unit fails)

	PR pch/13675
	* files.c (struct _cpp_file): Remove pch field.
	(pch_open_file): Don't set file->pch, just file->pchname.
	(should_stack_file): After pfile->cb.read_pch call
	free pchname and clear pchname, don't close file->fd.
	Test file->pchname instead of file->pch.  Don't close fd after cb.
	(_cpp_stack_include): Test file->pchname instead of file->pch.

	* c-pch.c (c_common_read_pch): On error close (fd) resp. fclose (f).

From-SVN: r133790