build: Sign all Windows binaries.

* build-aux/speedo.mk (AUTHENTICODE_SIGNHOST): New.
(AUTHENTICODE_TOOL): New.
(AUTHENTICODE_FILES): New.
(installer): Sign listed files.
(AUTHENTICODE_SIGNHOST): New macro.
(sign-installer): Use that macro instead of direct use of osslsigncode.

This also adds code to support signing via a Token. Because there is
no specification of that token, I was not able to write a free driver
for it. Thus we resort to use a running Windows-10 instance with an
enabled ssh server to do the code signing.

• Signed-off-by: Werner Koch <wk@gnupg.org>