server : fix building and simplify lib deps on Windows (#1772)

server : fix building and simplify lib deps on Windows (#1772)

* make : fix server example building on MSYS2 environments (Windows)

It was not working since commit eff3570f78742dfd56024328ed93d4f442434280
when server was introduced.

* cmake : simplify server example lib deps on Windows

server uses httplib::Server, not httplib::SSLServer, so there is no need
to mention cryptographic libraries in target_link_libraries.
Winsock (ws2_32) suffices here.

Also use plain library names like we use in other places.