Fix Vista CI and add a Vista DLL target (3_6_x branch)
This is similar to !1279 (merged) but on top of the current gnutls_3_6_x
branch instead of master. The code is exactly the same.
There was a typo in the original Vista addition so it did the same build as the non Vista target.
Also adding a Vista DLL (64 bits) target that may trigger the #1020 (closed) issue.
Edited by Dmitry Baryshkov