[DOC] Note that rb_obj_freeze_inline() can raise NoMemoryError

And move it back to a public header because Doxygen might not be
scanning the .c files.

[Feature #18776]

include/ruby/internal/fl_type.h

@@ -906,6 +906,14 @@ RB_OBJ_FROZEN(VALUE obj)
 }
 
 RUBY_SYMBOL_EXPORT_BEGIN
+/**
+ * Prevents further modifications to the given object.  ::rb_eFrozenError shall
+ * be raised if modification is attempted.
+ *
+ * @param[out]  x               Object in question.
+ * @exception   rb_eNoMemError  Failed   to   allocate memory  for  the  frozen
+ *                              representation of the object.
+ */
 void rb_obj_freeze_inline(VALUE obj);
 RUBY_SYMBOL_EXPORT_END
 

variable.c

@@ -1806,12 +1806,6 @@ rb_shape_set_shape_id(VALUE obj, shape_id_t shape_id)
     return true;
 }
 
-/**
- * Prevents further modifications to the given object.  ::rb_eFrozenError shall
- * be raised if modification is attempted.
- *
- * @param[out]  x  Object in question.
- */
 void rb_obj_freeze_inline(VALUE x)
 {
     if (RB_FL_ABLE(x)) {