Implement rb_gc_register_mark_object

Author: chrisseaton

lib/truffle/truffle/cext.rb

@@ -1410,6 +1410,12 @@ def rb_gc
     GC.start
   end
 
+  GC_ROOTS = []
+
+  def rb_gc_register_mark_object(obj)
+    GC_ROOTS.push obj
+  end
+
   def rb_nativethread_self
     Thread.current
   end

src/main/c/cext/ruby.c

@@ -4715,7 +4715,7 @@ void rb_define_virtual_variable(const char *name, VALUE (*getter)(ANYARGS), void
 }
 
 void rb_gc_register_mark_object(VALUE obj) {
-  rb_tr_error("rb_gc_register_mark_object not implemented");
+  RUBY_CEXT_INVOKE("rb_gc_register_mark_object", obj);
 }
 
 ID rb_check_id(volatile VALUE *namep) {