[CM] Snd 20.9 fails on Cygwin when compiled without GUI support

[bil at ccrma.Stanford.EDU]

It looks like it's trying to load libc_s7.so as a
scheme source file.  I haven't used cygwin, but
googling a bit, I think cygwin uses Windows .dll files,
not .so files.  I don't know how to load .dll files
dynamically.  I noticed that the -noinit flag
doesn't always fallback on the "dumb" repl --
maybe Snd needs a --dumb-repl switch.