use _XOPEN_SOURCE instead of manually prototyping wcwidth, also avoids a

conflict in musl

llt/utf8.c

@@ -12,6 +12,7 @@
   valid.
   A UTF-8 validation routine is included.
 */
+#define _XOPEN_SOURCE 700
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>

llt/utf8.h

@@ -16,7 +16,7 @@ typedef unsigned long long u_int64_t;
 
 extern int locale_is_utf8;
 
-#if defined(__WIN32__) || defined(__linux__)
+#if defined(__WIN32__)
 extern int wcwidth(uint32_t);
 #endif