This should be fixed by the upstream change in xdm 1.12 to use sed instead of cpp to generate the Xsession file:
https://gitlab.freedesktop.org/xorg/app/xdm/-/commit/5f941a815b7bad49a766987660094b01046c8e7d -- -Alan Coopersmith- alan.coopersm...@oracle.com Oracle Solaris Engineering - https://blogs.oracle.com/solaris
