Currently only available for the OpenSSL backend to use but doesn't
actually rely on anything OpenSSL specific.
Move it so it can be used by the Schannel backend in an upcoming patch
Change-Id: Ia29b153bf3f29cff0d62a41ec5dd7d4671a18095
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>