recovery: Add the missing #include.
Although I checked there's no reference to 'stage' in device-specific
recovery codes (for commit a8d72bc3b4087632e8cdad95e8355a2495e15690),
it's insufficient to capture the missing #include issue.
Test: lunch aosp_dragon-userdebug; mmma bootable/recovery
Change-Id: I4c5dbe9acf38918491c3aa776ce358be03f9ecca
diff --git a/common.h b/common.h
index 3e5f547..bda7935 100644
--- a/common.h
+++ b/common.h
@@ -20,6 +20,8 @@
#include <stdio.h>
#include <stdarg.h>
+#include <string>
+
#define STRINGIFY(x) #x
#define EXPAND(x) STRINGIFY(x)