py, unix: Allow to compile with -Wunused-parameter.

See issue #699.
diff --git a/py/emitglue.c b/py/emitglue.c
index 587c738..7064cb8 100644
--- a/py/emitglue.c
+++ b/py/emitglue.c
@@ -92,6 +92,8 @@
     fwrite(fun_data, fun_len, 1, fp_write_code);
     fclose(fp_write_code);
 #endif
+#else
+    (void)fun_len;
 #endif
 }
 #endif