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

[Jerome Guitton]

Christopher Faylor (cgf-use-the-mailinglist-please@sourceware.org):

> I wasn't entirely sure what was decided for Cygwin but Cygwin
> environment variables are meant, like Linux, to be case sensitive.
> Please keep that in mind when implementing this.  The CYGWIN=upcaseenv
> is a special case and not something that you should have to worry about.

Right, but when GDB creates the inferior it first convert the Cygwin
environment to Win32 (using CW_CVT_ENV_TO_WINENV) and then uses
directly CreateProcess. So it seems that the the case sensitivity is
lost in the process...