Use the RUNCMD mechanism also for osslsigncode.
* src/gpg4win.mk.in (AUTHENTICODE_sign): Use RUNCMD. * build.sh (runner_cmd_gpg_authcode_sign): New cmd.
Note that this expected a recent gpg-authcode-sign.sh script as
commited to GnuPG with 5ac8446ca8bf3fc3b1f41ffd91eb998034f9c5a8