make the interpreter platform

but still using the risc_instruction stream

test/arm/test_arm_platform.rb

@@ -0,0 +1,18 @@
+require_relative "helper"
+
+module Arm
+  class TestArmPlatform < MiniTest::Test
+    def setup
+      @arm = Risc::Platform.for("Arm")
+    end
+    def test_platform_class
+      assert_equal Arm::ArmPlatform , @arm.class
+    end
+    def test_platform_translator_class
+      assert_equal Arm::Translator , @arm.translator.class
+    end
+    def test_platform_loaded_class
+      assert_equal Fixnum , @arm.loaded_at.class
+    end
+  end
+end