[Ada] Update entities on class-wide condition function creation

[Pierre-Marie de Rodat]

Problem: Expression functions that have class-wide pre/post conditions
which call functions that are themselves expression functions refer to
entities from a specification that isn't theirs.

Solution: When creating the class-wide clone of the function that has
the class-wide condition, update its entities to refer to the right
spec.

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

gcc/ada/

	* sem_util.adb (Build_Class_Wide_Clone_Body): Update entities to
	refer to the right spec.
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