libsframe: provide new access API for mangled RA bit

include/ChangeLog:

	* sframe-api.h (sframe_fre_get_ra_mangled_p): New declaration.

ChangeLog:

	* libsframe/sframe.c (sframe_get_fre_ra_mangled_p): New
	definition.
	(sframe_fre_get_ra_mangled_p): New static function.