bug#32658: gnutls + non-blocking url-retrieve

[thomas]

Hi,

some more details.

1.) I needed to revert to gnutls 3.5.19, the mingw64 build from the
gitlab ci build seems to have a working gnutls-cli tools on windows 10.
the gitlab builds for 3.6.3 and 3.6.4 seems to have another bug
(error code -53) in the gnutls-cli command.

so only gnutls 3.5.19 have a working gnutls-cli. i installed this version in 
emacs 26.1

2.) testing gnutls stream
using open-gnutls-stream directly gives me a correct tls connection but
eww still fails to load the site.

when I change url-open-stream in url/url-gw.el to:
                          (open-network-stream
                           name buffer host service
                           :type gw-method
                           ;; Use non-blocking socket if we can.
                          :nowait nil))

I finally can open lwn.net in eww.

so something seems to be wrong possible with blocking/non-blocking
network access.

any ideas?