io.c: export rb_io_extract_modeenc

* include/ruby/io.h (rb_io_enc_t): add typedef.

* io.c (rb_io_extract_modeenc): export.

include/ruby/io.h

@@ -101,6 +101,8 @@ typedef struct rb_io_t {
     VALUE write_lock;
 } rb_io_t;
 
+typedef struct rb_io_enc_t rb_io_enc_t;
+
 #define HAVE_RB_IO_T 1
 
 #define FMODE_READABLE              0x00000001
@@ -153,6 +155,7 @@ int rb_io_wait_writable(int);
 int rb_wait_for_single_fd(int fd, int events, struct timeval *tv);
 void rb_io_set_nonblock(rb_io_t *fptr);
 int rb_io_extract_encoding_option(VALUE opt, rb_encoding **enc_p, rb_encoding **enc2_p, int *fmode_p);
+void rb_io_extract_modeenc(VALUE *vmode_p, VALUE *vperm_p, VALUE opthash, int *oflags_p, int *fmode_p, rb_io_enc_t *convconfig_p);
 ssize_t rb_io_bufwrite(VALUE io, const void *buf, size_t size);
 
 /* compatibility for ruby 1.8 and older */

io.c

@@ -5864,7 +5864,7 @@ extract_binmode(VALUE opthash, int *fmode)
     }
 }
 
-static void
+void
 rb_io_extract_modeenc(VALUE *vmode_p, VALUE *vperm_p, VALUE opthash,
         int *oflags_p, int *fmode_p, convconfig_t *convconfig_p)
 {