emulators/libretro-bsnes: Update to v115.a.20231101

Also remove dependency on GCC ports: this makes it easier to update
GCC_DEFAULT. Moreover, the port now builds with lang/gcc13.

Set PORTEPOCH to use a version scheme more consistent with
https://docs.freebsd.org/en/books/porters-handbook/book/#makefile-master_sites-github

PR: 273678
Approved by: Timothy Beyer <beyert@cs.ucr.edu>