[RFA/mingw32] environment variables are case-insensitive on win32

[Jerome Guitton]

Corinna Vinschen (vinschen@redhat.com):

> Probably an old Cygwin version.  Older versions of Cygwin did not
> honor the case of env vars, but rather converted them all to uppercase,
> but this is pre-2008!

Not so old actually, this is 1.7.9.


> I don't have GDB test environment set up, but this works for me with the
> most recent Cygwin version 1.7.18.

Probably something wrong in my setup then. So the last patch that I
submitted (today) is the proper one.