Revert "Hide most of the implementation of `struct rb_io`. (#6511)"

This reverts commit 18e55fc1e1ec20e8f3166e3059e76c885fc9f8f2.

fix [Bug #19704]
https://bugs.ruby-lang.org/issues/19704
This breaks compatibility for extension libraries. Such changes
need a discussion.

1 files changed, 1 insertions, 0 deletions

diff --git a/file.c b/file.c
index 5f59373a45..2c74f3eff5 100644
--- a/file.c
+++ b/file.c
@@ -169,6 +169,7 @@ int flock(int, int);
 #include "internal/thread.h"
 #include "internal/vm.h"
 #include "ruby/encoding.h"
+#include "ruby/io.h"
 #include "ruby/thread.h"
 #include "ruby/util.h"