Only add Builtin methods that are not in the current compilation

Current bug looks like the original main is used in parts
(not the compiled one, but the builtin on)

test/mom/test_mom_compiler.rb

@@ -15,6 +15,9 @@ module Mom
     def test_compilers
       assert_equal 24 , @comp.method_compilers.length
     end
+    def test_compilers_bare
+      assert_equal 23 , MomCompiler.new.method_compilers.length
+    end
     def test_returns_constants
       assert_equal Array , @comp.constants.class
     end

test/mom/test_mom_compiler1.rb

@@ -32,7 +32,7 @@ module Mom
       assert_equal Risc::Label , @linker.assemblers.first.instructions.class
     end
     def test_assembler_assembled
-      assert_equal Risc::SlotToReg , @linker.assemblers.first.instructions.next.class
+      assert_equal Risc::LoadConstant , @linker.assemblers.first.instructions.next.class
     end
     def test_no_loops_in_chain
       @linker.assemblers.each do |asm|