make compilation faster on Windows

[Simon Josefsson]

Vincent Torri <vincent.torri at gmail.com> writes:

> Hey,
>
> by default, the header file windows.h includes a *lot* os other header
> files, which are almost always useless, except in some cases of course. It
> improves the compilation speed, especially with MSYS/MinGW.
>
> There is a way to reduce the number of header files included by windows.h:
>
> #define WIN32_LEAN_AND_MEAN
> # include <windows.h>
> #undef WIN32_LEAN_AND_MEAN
>
> You can look at windows.h to see what the macro WIN32_LEAN_AND_MEAN disable.
>
> As far as I can see, 2 files are using windows.h in gnutls/src: crypt.c and
> psk.c

I suspect a better fix is to just remove the '#include <windows.h>', as
we use gnulib modules for Windows portability.  I'll try a Windows build
to see if this works...

/Simon