Revert "xcursor: use strncat instead of strncpy"

This reverts commit 7dffe9339b, which introduced
another linter error with -O3:

  error: ‘strncat’ specified bound 7 equals source length [-Werror=stringop-overflow=]

This makes sense because strncat(dest, "cursors", strlen("cursors")) is moot
in security point of view.

The next commit will replace strncpy() with memcpy(), so let's restore the
original implementation.

xcursor/xcursor.c

@@ -655,7 +655,11 @@ _XcursorAddPathElt (char *path, const char *elt, int len)
 	elt++;
 	len--;
     }
-    strncat (path + pathlen, elt, len);
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstringop-truncation"
+    strncpy (path + pathlen, elt, len);
+    path[pathlen + len] = '\0';
+#pragma GCC diagnostic pop
 }
 
 static char *