Remove copied sources

Makefile.in

@@ -347,6 +347,7 @@ clean:
 	@$(RM) -r lib include/bits
 	$(RM) lib*/*.a ldso/*/*.a libpthread/*/*.a
 	$(RM) libc/misc/internals/interp.c
+	$(RM) libc/stdio/*64.c
 	$(RM) include/fpu_control.h include/dl-osinfo.h
 	$(MAKE) -C extra/locale clean
 	$(MAKE) -C ldso headers_clean-y