dnl ...
dnl With the autoconf I produce for VMS, this is very possible. -- Richard L.
AC_INSTALL_EXTRA_ARG(--startupdir=DIR,startupdir,dnl
-STARTUPDIR/--ST*ARTUPDIR=,STARTUPDIR,
[--startupdir=DIR	defines the directory for the startup database],
[SYS$COMMON:[SYS$STARTUP]])dnl
AC_INSTALL_EXTRA_prsub(startupdir)dnl
dnl
AC_INIT(...)
dnl ...
AC_OUTPUT([dnl
dnl ...
dnl ...
])