Use O_CLOEXEC instead of O_RDONLY to signal loopfiles_rw() to close filehandles.
diff --git a/toys/posix/cmp.c b/toys/posix/cmp.c
index 13990d4..2dae113 100644
--- a/toys/posix/cmp.c
+++ b/toys/posix/cmp.c
@@ -79,6 +79,6 @@
 
 void cmp_main(void)
 {
-  loopfiles_rw(toys.optargs, O_RDONLY, 0, toys.optflags&FLAG_s, do_cmp);
+  loopfiles_rw(toys.optargs, O_CLOEXEC, 0, toys.optflags&FLAG_s, do_cmp);
 }