fix iar build with board_test

examples/device/board_test/src/tusb_config.h

@@ -30,6 +30,11 @@
  extern "C" {
 #endif
 
+// board_test example is special example that doesn't enable device or host stack
+// This can cause some TinyUSB API missing, this define hack to allow us to fill those API
+// to pass the compilation process
+#define tud_int_handler(x)
+
 //--------------------------------------------------------------------
 // COMMON CONFIGURATION
 //--------------------------------------------------------------------