ada: Reject conditional goto in lock-free protected subprograms

ada: Reject conditional goto in lock-free protected subprograms

In lock-free protected subprograms we don't allow goto statements;
likewise, we now reject conditional goto statements.

This fix only affects semantic checking mode with switch -gnatc.
In ordinary compilation we already rejected conditional goto after
it was expanded into ordinary goto.

gcc/ada/

	* sem_ch9.adb (Allows_Lock_Free_Implementation): Reject
	conditional goto statements.