Mark broken when USE_GCC=9. Upstream git commit
63e9edcb6084d4b164439065e2d71f3e900ec3c7 resolves this issue.
Unfortunately it does not apply, requiring this port to be upated to
ksh93 well into ksh93-devel. Bringing ksh93 up to the ksh93-devel or
shy of it would negate the justification for ksh93's existence. It is
therefore recommended that people use ksh93-devel on architectures that
use GCC 9 or use GCC 8.

PR: 239644
Reported by: pkubaj@