Attempt to fix build problems under Solaris (11 at least) if the "drac"
option is used.

Problem reported by Richard Palo in PR pkg/47420.
Tim Mann allegedly suggested disabling HAVE_SIGIO for hanging xtrs on
Linuxes 5 years ago. I see the same problem on NetbSD-6 (at least; didn't
try older) and the same cure works.
Actually install the provided utility disk images with the emulator, so
that we can swap files back and forth with TRS/80 disk operating systems.