x11-wm/stumpwm: Fix build when stumpwm is already installed

When the stumpwm package was already installed and loaded, asdf used output
translation to write the generated fasl files directly to
${PREFIX}lib/common-lisp/stumpwm/sbclfasl. Use the solution described and
implemented in ${PREFIX}/etc/asdf-init.lisp (installed by devel/cl-asdf),
which allows the installed lisp packages to be loaded and the fasl files to
be written to ${WRKSRC}.

PR: 251602
Reported by: Aleksandr Konkov <konkovaa@hotmail.com>