ports-gcc: add missing header

Index: src/ime.cpp
--- src/ime.cpp.orig
+++ src/ime.cpp
@@ -3,6 +3,7 @@
 #define Uses_SCIM_CONFIG_BASE
 #define Uses_SCIM_CONFIG_PATH
 #include <ctype.h>
+#include <string.h>
 
 #include <scim.h>
 #include "scim_fcitx_imengine.h"