[Ada] Fix bogus discriminant check failure for type with predicate

[Ada] Fix bogus discriminant check failure for type with predicate

This reorders the processing in Freeze_Entity_Checks so that building the
predicate functions, which first requires building discriminated checking
functions for record types with a variant part, is done after processing
and checking this variant part.

gcc/ada/

	* sem_ch13.adb (Freeze_Entity_Checks): Build predicate functions
	only after checking the variant part of a record type, if any.