Simple (?) Windows question

[Robert Goldman]

Is there some way that a CL implementation can know whether it is
running under a Unix-alike like Cygwin or MinGW?

If we use RUN-PROGRAM to interrogate the environment, we do so using
CMD.exe, so I'm not sure how CMD.EXE would know if it was being run as
the grandchild of a bash process.

AFAICT Cygwin (and I don't know about MinGW) don't put anything into
their environments that I can obviously see.  E.g., if I start a lisp
inside cygwin and do (GETENV "OS") I just see "Windows_NT".

Thanks,
r