devel/freebsd-sysroot: force rebuild with pkg 2.7.1

pkg 2.7.1 will make sure at installation this port is not expecting
any shlib to be required to the exception of the private libraries
which are not part of this sysroot, but some of the libraries in this
sysroot are linked to those libprivate so they are listed in the
required field, add NO_SHLIB_REQUIRES_GLOB=libprivate* to get rid of
those.

PR: 293874