ada: Fix pragma Compile_Time_Error and -gnatdJ crash

This patch makes it so the diagnostics coming from occurrences of
pragma Compile_Time_Error and Compile_Time_Warning are emitted with
a node parameter so they don't cause a crash when -gnatdJ is enabled.

gcc/ada/

	* errout.ads (Error_Msg): Add node parameter.
	* errout.adb (Error_Msg): Add parameter and pass it to
	the underlying call.
	* sem_prag.adb (Validate_Compile_Time_Warning_Or_Error): Pass
	pragma node when emitting errors.