Fix rb_errno_ptr

Author: sue445

_tools/ruby_h_to_go/lib/ruby_h_to_go/generator_helper.rb

@@ -123,7 +123,12 @@ def ruby_pointer_c_type_to_go_type(typename, pos:, pointer:)
         return "unsafe.Pointer"
       end
 
-      go_type_name = ruby_c_type_to_go_type(typename, pos:, pointer: nil)
+      go_type_name =
+        if typename == "int" && %i[return typeref].include?(pos)
+          "Int"
+        else
+          ruby_c_type_to_go_type(typename, pos:, pointer: nil)
+        end
 
       case pointer
       when :array

_tools/ruby_h_to_go/spec/ruby_h_to_go/function_definition_spec.rb

@@ -188,8 +188,8 @@
           // Original definition is following
           //
           //	int *rb_errno_ptr(void)
-          func RbErrnoPtr() *int {
-          ret := (*int)(C.rb_errno_ptr())
+          func RbErrnoPtr() *Int {
+          ret := (*Int)(C.rb_errno_ptr())
           return ret
           }