Fix to bug 25504 for gnutls based schannel

[Hans Leidekker]

On Sun, 2011-04-17 at 09:42 -0400, jbalentine at tuffmail.com wrote:
>  #ifdef SONAME_LIBGNUTLS
>  #include <gnutls/gnutls.h>
> +#include <gcrypt.h>
> +#include <pthread.h>
> +#include <errno.h>
> +GCRY_THREAD_OPTION_PTHREAD_IMPL; 

You should add a separate configure check for libgcrypt. Use of pthreads
reveals an implementation detail of Wine threads, I think it would be
cleaner to supply Win32 implementations of the locking functions via
GCRY_THREAD_OPTION_USER.