BSD grep from FreeBSD for Linux.

Imported from freebsd-src, commit caf5283 (Sep 2023); this became the default grep in FreeBSD 13:

Switch to the BSDL grep implementation now that it's been a little more thoroughly tested and theoretically supports all of the extensions that gnugrep in base had with our libregex(3).

Folks shouldn't really notice much from this update; bsdgrep is slower than gnugrep, but this is currently the price to pay for fewer bugs. Those dissatisfied with the speed of grep and in need of a faster implementation should check out what textproc/ripgrep and textproc/the_silver_searcher can do for them.

Run update.sh to update the sources, and use the standard make and make install to install it.

Only [efr]?grep is installed by default; use make install-zgrep to install zgrep and all the many links to it (bzgrep, zfgrep, zstdegrep, etc.).

make check runs the tests (zsh is required).