This occurs because protected subprograms are not translated directly into
object code but first rewritten as a pair of subprograms by the front-end.

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

gcc/ada/

	* exp_ch9.adb (Build_Protected_Spec): Tidy up and propagate the
	Comes_From_Source flag onto the new formal parameters.
	* sem_ch6.adb (Analyze_Subprogram_Body_Helper): Do not check
	references for subprograms generated for protected subprograms.