Ada: Add missing guard before accessing the Underlying_Record_View field

It is necessary when GNAT extensions are enabled (-gnatX switch).

gcc/ada/
	PR ada/121056
	* sem_ch4.adb (Try_Object_Operation.Try_Primitive_Operation): Add
	test on Is_Record_Type before accessing Underlying_Record_View.

gcc/testsuite/
	* gnat.dg/deref4.adb: New test.
	* gnat.dg/deref4_pkg.ads: New helper.
3 files changed