Create a link for the proxy module.

Create a link for the proxy module.

 * Install proxy module at its own path which is not prefixed by 'lib'
 * Since the proxy module is the same as the library, and actually
   needs to be loaded as the same library in memory (due to resource
   tracking per process), use a symlink for proxy.
 * Add a variable to the pkg-config file which shows the path
   to the proxy module. ie:
   $ pkg-config --variable=proxy_module p11-kit-1

https://bugzilla.redhat.com/show_bug.cgi?id=725905