Why this message "kernel is missing COMPAT_FREEBSD11"

Dear RISC-V types :

     I have been watching my SiFive board grind away slowly with
poudriere for a while and today I saw this message about emacs:

[01] [00:10:20] Skipping editors/emacs@full | emacs-29.4,3: Dependent 
port lang/rust | rust-1.81.0 failed


     This of course will tell me that something went wrong when trying to
build rust. Somewhere. Somehow.  Thankfully there is a detailed log file
on this Friday the 13th wherein I see :


=======================<phase: configure      >============================
===== env: NO_DEPENDS=yes USER=root UID=0 GID=0
===>  Configuring for rust-1.81.0
===>   FreeBSD 10 autotools fix applied to 
/wrkdirs/usr/ports/lang/rust/work/rustc-1.81.0-src/vendor/libssh2-sys-0.3.0/libssh2/config.rpath
===>   FreeBSD 10 autotools fix applied to 
/wrkdirs/usr/ports/lang/rust/work/rustc-1.81.0-src/vendor/libssh2-sys-0.2.23/libssh2/config.rpath
Bad system call
=> Sanity check failed: kernel is missing COMPAT_FREEBSD11
=> Aborting build
*** Error code 1

Stop.
make: stopped making "configure" in /usr/ports/lang/rust
=>> Cleaning up wrkdir
===>  Cleaning for rust-1.81.0
build of lang/rust | rust-1.81.0 ended at Fri Sep 13 02:04:27 UTC 2024
build time: 00:10:20
!!! build failure encountered !!!


Well gee. Does this mean I need to stop everything and do a build of the
kernel with some magic config variable "COMPAT_FREEBSD11" in some magic
file somewhere?


--
Dennis Clarke
RISC-V/SPARC/PPC/ARM/CISC
UNIX and Linux spoken