[Preprocessor] small cleanups

[Preprocessor] small cleanups

https://gcc.gnu.org/ml/gcc-patches/2019-08/msg01904.html
	* directives-only.c (_cpp_preprocess_dir_only): Use false, not
	zero for _cpp_handle_directive call.
	* directives.c (_cpp_handle_directive): Indented is bool.
	* files.c (struct _cpp_file): Make bools 1 bit bitfields.
	* internal.h (enum include_type): Reformat and comment.
	(struct cpp_buffer): Make flags 1 bit bitfields.
	(_cpp_handle_directive): Indented is bool.

From-SVN: r274999