How do I set the version for my platform?

[Jason House]

Ok, that may sound like a stupid question, but gdc -fversion=Win32 yields:
"Error: version identifier 'Win32' is reserved and cannot be set"

If I don't do that, I tango outputs
"Unsupported environment; neither Win32 or Posix is declared"

I assume I'm doing something really stupid, like not setting a config file.  Any help would be appreciated.