libmicrohttpd: add dependency on file and disable spdy

* fixes following floating dependencies:
  libmicrohttpd/libmicrohttpd-bin/latest lost dependency on  file
  WARN: libmicrohttpd rdepends on libssl but it isn't a build dependency? [build-deps]

* and unknown-configure-option qa warning:
  libmicrohttpd-0.9.34: libmicrohttpd: configure was passed
    unrecognised options: --enable-gnutls [unknown-configure-option]

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>