Define HAVE_SSL_GET_SHUTDOWN when available (Windows) #4100
Just noticed, that the following code fragment in lib/vtls/openssl.c is disabled in the Windows build because HAVE_SSL_GET_SHUTDOWN is undefined, but shouldn't be:
I'm not sure in which OpenSSL version SSL_get_shutdown() was first introduced, but according to the docs it is at least available beginning with 1.0.2.
The patch follows the implementation strategy of other HAVE_* defines found in openssl.c, like HAVE_X509_GET0_SIGNATURE. If this is not the right approach, feel free to change.