ada: Spurious reference warning on qualified expression

ada: Spurious reference warning on qualified expression

This patch fixes an error in the compiler whereby an assignment to an out
formal (whose type requires a predicate check) can lead to spurious
"value may be referenced before it has a value" warnings when the RHS is a
qualified expression.

gcc/ada/

	* sem_warn.adb (Within_Postcondition): Add case to ignore
	references within generated predicate function calls.