c-common.h (tree_dump_index): Add more comments.

c-common.h (tree_dump_index): Add more comments.

	* c-common.h (tree_dump_index): Add more comments.
	* c-dump.c (dump_files): Name flags `tree' rather than `ast'.
	(dump_option_value_info): New struct.
	(dump_options): New array.
	(dump_switch_p): Parse switch options symbolically.
	* doc/invoke.texi (-fdump-ast): Rename to ...
	(-fdump-tree): ... here. Document that options are symbolic, and
	not all are applicable.

From-SVN: r45373