Change m2 lexical analysis to optionally consume C comments.

Change m2 lexical analysis to optionally consume C comments.

This patch allows a subsequent patch to turn on/off the consuming
of C comments.

gcc/m2/ChangeLog:

	* m2.flex (cpreprocessor): Add temporary variable
	which is initialized to 0.
	(commentCLevel): New variable.
	(endOfCComment): New function.
	(splitSlashStar): New function to split /* into / and *
	tokens.
	(COMMENTC): New flex state.
	("/*"): New rule to test whether we should treat /*
	as a single token or as two tokens.
	(<COMMENTC>.): New rule to skip a character.
	(<COMMENTC>\n.*): New rule to consume the line.
	(<COMMENTC>"*/"): New rule to call endOfCComment.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>