Upstream patch: fix build for Hurd (#52) (closes: #1009066)

Upstream patch: fix build for Hurd (#52) (closes: #1009066)

Since d5a61ee8 (Patch to detect (and ignore) symlink loops in
pcre2grep., 2021-08-28), there is optional code that depends
on readlink and PATH_MAX but that had only detection added for
the first.

GNU Hurd doesn't have the later so it fails to build.

Improve the detection to include both dependencies in autotools
and cmake to fix that.

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Signed-off-by: Matthew Vernon <matthew@debian.org>