Add cleanup of *.s

Reviewed-by: Matt Caswell <matt@openssl.org>

crypto/ec/Makefile

@@ -89,7 +89,7 @@ dclean:
 	mv -f Makefile.new $(MAKEFILE)
 
 clean:
-	rm -f *.o */*.o *.obj lib tags core .pure .nfs* *.old *.bak fluff
+	rm -f *.s *.o */*.o *.obj lib tags core .pure .nfs* *.old *.bak fluff
 
 # DO NOT DELETE THIS LINE -- make depend depends on it.