drop-in type check for rb_define_singleton_method

We can check the function pointer passed to
rb_define_singleton_method like how we do so in rb_define_method.
Doing so revealed many arity mismatches.

1 files changed, 1 insertions, 1 deletions

diff --git a/io.c b/io.c
index 827903476e..6ae2ee5ff9 100644
--- a/io.c
+++ b/io.c
@@ -7042,7 +7042,7 @@ rb_io_s_open(int argc, VALUE *argv, VALUE klass)
  */
 
 static VALUE
-rb_io_s_sysopen(int argc, VALUE *argv)
+rb_io_s_sysopen(int argc, VALUE *argv, VALUE _)
 {
     VALUE fname, vmode, vperm;
     VALUE intmode;