regexp: Import change from JimTcl.
* regexp/jimregexp.h, regexp/jimregexp.c: Fix from JimTcl.
Apply the change in JimTcl:
commit ac35b8a6ec417f75b5ec86ca64ea1614a8170a38 Author: Steve Bennett <steveb@workware.net.au> Date: Mon May 4 20:43:46 2020 +1000 regexp: Improved error message
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>