turn recovery into a C++ binary

Change-Id: I68a67a4c8edec9a74463b3d4766005ce27b51316
diff --git a/recovery_ui.h b/recovery_ui.h
index 5f01770..4c4baf5 100644
--- a/recovery_ui.h
+++ b/recovery_ui.h
@@ -19,6 +19,10 @@
 
 #include "common.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 // Called before UI library is initialized.  Can change things like
 // how many frames are included in various animations, etc.
 extern void device_ui_init(UIParameters* ui_parameters);
@@ -84,4 +88,8 @@
 // Text of menu items.
 extern char* MENU_ITEMS[];
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif