cmpdisk.exe is a DOS program. See doc/testing.doc for details.
The sources are in cmpdisk.cpp. You must compile them under DOS.
As not everyone is expected to have a DOS C compiler the BC 3.1 compiled
(16bit) executable is included here.
Yes, there is also a GCC port for DOS. There are even two. Search the net
for 'djgpp' or 'emx'. But they are 32 bit (i.e. overkill for this small
program). But it should also work though the program has not been tested
with recent versions.
If I remember correctly, the FREEDOS project has a free DOS C compiler,
or has at least pointers to one. I promise to test it some day and replace
the BC compiled executable by one compiled with a free compiler. Note that
this is not a license problem. It's just a kind of "political" question
concerning free software :)