PR fortran/95980 - ICE on using sync images with -fcheck=bounds

PR fortran/95980 - ICE on using sync images with -fcheck=bounds

In SELECT TYPE, the argument may be an incorrectly specified unlimited
polymorphic variable.  Avoid a NULL pointer dereference for clean error
recovery.

gcc/fortran/
	PR fortran/95980
	* match.c (copy_ts_from_selector_to_associate, build_class_sym):
	Distinguish between unlimited polymorphic and ordinary variables
	to avoid NULL pointer dereference.
	* resolve.c (resolve_select_type):
	Distinguish between unlimited polymorphic and ordinary variables
	to avoid NULL pointer dereference.

(cherry picked from commit f2151227dfe90a5fe73297c370786be98b0b090f)