lang/sbcl: Backport fix for SBCL bug #2090967

A change introduced in SBCL 2.4.11 caused build failures for downstream
projects such as StumpWM. For details, see:
https://bugs.launchpad.net/sbcl/+bug/2090967.

Backport a fix from the SBCL master branch to address the build issue
for x11-wm/stumpwm.

Approved by: krion (maintainer, via IRC)
Differential Revision: https://reviews.freebsd.org/D47995