In the case of a constrained access definition for a record component we
are calling create_itype twice the former not being updated.  This leads
to a malformed node that crashes -gnatG when predicates are activated.
Instead of creating a default Itype for Desig_Subtype, create it with
the correct scope in each case.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_ch3.adb (Constrain_Access): Call Desig_Subtype in each if
	branch to avoid calling it twice.