byacc: update to 20210109.

2021-01-09  Thomas E. Dickey  <dickey@invisible-island.net>

* package/debian/copyright, VERSION, package/byacc.spec,
package/debian/changelog, package/mingw-byacc.spec,
package/pkgsrc/Makefile: bump

2021-01-05  Thomas E. Dickey  <dickey@invisible-island.net>

* configure: regen

* aclocal.m4: resync with my-autoconf

2020-09-22  Thomas E. Dickey  <dickey@invisible-island.net>

* closure.c, warshall.c:
fix undefined-behavior diagnosed with gcc -fsanitize=undefined
(report by Alexander Richardson)

(fcambus)