clean up some warnings when building recovery

Change-Id: I1541534ee6978ddf8d548433986679ce9507d508
diff --git a/edify/expr.h b/edify/expr.h
index 0d8ed8f..a9ed2f9 100644
--- a/edify/expr.h
+++ b/edify/expr.h
@@ -164,6 +164,8 @@
 // Free a Value object.
 void FreeValue(Value* v);
 
+int parse_string(const char* str, Expr** root, int* error_count);
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif