configure.ac: disable SPDY by default on W32
configure.ac: disable SPDY by default on W32

ghaderer/libmicrohttpd,maru/libmicrohttpd-http2,maru/libmicrohttpd-http2,ghaderer/libmicrohttpd,ghaderer/libmicrohttpd,maru/libmicrohttpd-http2