Fixed RasPi builds of unit tests.

On RasPi with gcc 4.8.2, the asserts wouldn't compile when tests were enabled.
Enforced the assumption that ASSERT code is generated only in Debug builds.

src/Entities/ArrowEntity.cpp

@@ -67,7 +67,9 @@ bool cArrowEntity::CanPickup(const cPlayer & a_Player) const
 		case psInCreative:           return a_Player.IsGameModeCreative();
 	}
 	ASSERT(!"Unhandled pickup state");
-	return false;
+	#ifndef __clang__
+		return false;
+	#endif
 }