contrib/bc upgrade to version 7.1.0
This update fixes a few bugs:
- Improper response to double SIGINT with editline.
- Not letting libedit handle terminal size changes.
- A dc crash from improperly handling an error.
- A duplicate check for reference arrays.
- Build failures with GCC 15.
Merge commit '682da5a0fdb2c38ecc3951047a882471d62aa1d1'