Log Message:
simh: update to 4.0.0.20180919

Update simh to a current git snapshot.  The main motivation for the
update is the fix to simh bug #478, which is needed for NetBSD to boot
on an emulated VAX under anita.  There have also been other changes
too numerous to list here, including the following new emulations:
3b2, i701, i7010, i704, i7070, i7080, i7090, scelbi, sigma, uc15.