Add a recursion limit to libiberty's demangling code.  The limit is enabled by default, but can be disabled via a new demangling option.

include	* demangle.h (DMGL_NO_RECURSE_LIMIT): Define.
        (DEMANGLE_RECURSION_LIMIT): Define

	PR 87681
	PR 87675
	PR 87636
	PR 87350
	PR 87335
libiberty * cp-demangle.h (struct d_info): Add recursion_level field.
	* cp-demangle.c (d_function_type): Add recursion counter.
	If the recursion limit is reached and the check is not disabled,
	then return with a failure result.
	(cplus_demangle_init_info): Initialise the recursion_level field.
        (d_demangle_callback): If the recursion limit is enabled, check
	for a mangled string that is so long that there is not enough
	stack space for the local arrays.
        * cplus-dem.c (struct work): Add recursion_level field.
	(squangle_mop_up): Set the numb and numk fields to zero.
	(work_stuff_copy_to_from): Handle the case where a btypevec or 
	ktypevec field is NULL.
	(demangle_nested_args): Add recursion counter.  If
	the recursion limit is not disabled and reached, return with a
	failure result.

From-SVN: r266886