New port emulators/libc6-shim

ABI-compatible glibc shim library

A shim library providing limited glibc ABI compatibility on top of FreeBSD libc.
It allows loading shared objects compiled on Linux and dynamically linked to
glibc into native FreeBSD processes.

PR: 250591
Submitted by: Alex S <iwtcex@gmail.com>
Reviewed by: ericbsd