Darcs on this system (Ubuntu) links against the openssl library via
libcurl, and it looks from configure.ac as though it can be linked
explicitly when configured for git.  The openssl licence is
incompatible with the GPL, so the binary isn't legally distributable.

While you can link with a libcurl built using gnutls rather than
openssl, it would be best to add an exception to the licence to allow
linking with openssl.  You could follow the exception used for GNU
wget:

  In addition, as a special exception, the Free Software Foundation
  gives permission to link the code of its release of Wget with the
  OpenSSL project's "OpenSSL" library (or with modified versions of it
  that use the same license as the "OpenSSL" library), and distribute
  the linked executables.  You must obey the GNU General Public License
  in all respects for all of the code used other than "OpenSSL".  If you
  modify this file, you may extend this exception to your version of the
  file, but you are not obligated to do so.  If you do not wish to do
  so, delete this exception statement from your version.