Configure libkleo with different GnuPG install dir registry key for VSD

* src/Makefile.am (gpg4win_pkg_libkleo_configure): New.
* src/gpg4win.mk.in (GNUPG_INSTALL_DIR_REGISTRY_KEY): New.

This ensures that Kleopatra (and other apps using libkleo) find the
correct GnuPG installation belonging to VSD. The values are plus-
escaped because space characters break the build spectacularly.

• GnuPG-bug-id: T7758