add abort() to non-reached code

This cleans up a lot of false-positives in static analysis
and also helps compilers to optimize code paths in general.
(tagging the fatal stingstream operator as ‘noreturn’ is
far less trivial)

libs/evoral/src/ControlList.cpp

@@ -1199,7 +1199,7 @@ ControlList::unlocked_eval (double x) const
 		return multipoint_eval (x);
 	}
 
-	/*NOTREACHED*/ /* stupid gcc */
+	abort(); /*NOTREACHED*/ /* stupid gcc */
 	return _default_value;
 }