Add mock file avr/interrupt.h in case anything includes it

Author: ianfixes

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Add util/atomic.h
 - `Logger` class to centralize CI runner script logging (in particular, indentation)
 - Explicit reporting of free bytes after compilation
+- `interrupt.h` mock
 
 ### Changed
 - `arduino_ci.rb` uses new `Logger`

cpp/arduino/avr/interrupt.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#define _VECTOR(N) __vector_ ## N
+#define SIGNAL ( vector )
+
+void cli() {};
+void sei() {};