maint: rely on Automake for parsers.

maint: rely on Automake for parsers.

	* Makefile.am (AM_YFLAGS): Automake looks for "-d" alone.
	Move other options in here.
	(BISON): New.
	(YACC): Use it.
	(bison_SOURCES): Now that automake can see `-d' in AM_YFLAGS,
	we can rely on it to compile and ship the parser header
	files.

Based on commit 737406a32c201471699bfa0843d1f432f3ec29ab and
commit 3d6ca339083c278d907c9f030f4ba6bc5ecb07f2.