make: fix GCC warnings

@@ -38,10 +38,12 @@
 #include <mksh/macro.h>
 #include <mksh/misc.h>          /* retmem() */
 #include <mksh/read.h>          /* get_next_block_fn() */
 #include <mksdmsi18n/mksdmsi18n.h>      /* libmksdmsi18n_init() */
 
+#include <widec.h>
+
 /*
  * File table of contents
  */
 static void     add_macro_to_global_list(Name macro_to_add);
 #ifdef NSE

@@ -862,11 +864,11 @@
         Macro_list      new_macro;
         Macro_list      macro_on_list;
         char            *name_on_list = (char*)NULL;
         char            *name_to_add = macro_to_add->string_mb;
         char            *value_on_list = (char*)NULL;
-        char            *value_to_add = (char*)NULL;
+        const char      *value_to_add = (char*)NULL;
 
         if (macro_to_add->prop->body.macro.value != NULL) {
                 value_to_add = macro_to_add->prop->body.macro.value->string_mb;
         } else {
                 value_to_add = "";