Fix multiple WWW-Authenticate headers

This patch fixes the case with the server trying to negociate the authentication
method and returning multiple WWW-Authenticate headers.
channels: fix link errors.
audin/server: fix a crash.
Merge pull request #1803 from hardening/www_authenticate_fix

Www authenticate fix
cmake: improve __FILE__ relative path hack
channels/cliprdr: fix cliprdr_process_format_data_response callback usage
Merge branch 'master' of github.com:FreeRDP/FreeRDP