fix missing exec permissions on replaced config.sub

Makefile

@@ -135,7 +135,7 @@ musl-git-%:
 	mkdir $@.tmp
 	( cd $@.tmp && find ../$< -path '*/*/*' -prune -exec sh -c 'ln -s "$$@" .' ':' {} + )
 	test ! -d patches/$@ || cat patches/$@/* | ( cd $@.tmp && $(COWPATCH) -p1 )
-	test ! -f $</config.sub || ( rm -f $@.tmp/config.sub && cp -f $(SOURCES)/config.sub $@.tmp/ )
+	test ! -f $</config.sub || ( rm -f $@.tmp/config.sub && cp -f $(SOURCES)/config.sub $@.tmp/ && chmod +x $@.tmp/config.sub )
 	rm -rf $@
 	mv $@.tmp $@