Update cl-loop-parser grammar file for bison 3.x

Update cl-loop-parser grammar file for bison 3.x

This allows the cl emodule to build with bison version 3.x, and sets
the minimum required version to 2.7

	* m4/sxe-bldchain-progs.m4 (SXE_PROG_BISON): Set minimum bison
	version needed to v2.7.x,

	* modules/cl/cl-loop-parser.y: Use api.prefix, api.pure instead of
	name-prefix, pure_parser which are deprecated.

Signed-off-by: Steve Youngs <steve@sxemacs.org>