bug#35629: 27.0.50; version-to-list fails on Cygwin gpg2 version string

[Kazuhiro Ito]

Cygwin's gpg2 has "-unknown" suffix in version string.

> $ gpg2 --version
>
> gpg (GnuPG) 2.2.15-unknown
> ...

version-to-list function fails to parse this version string and
epg-find-configuration can't find gpg2 as supported one.

(epg-find-configuration 'OpenPGP t)
-> ((program . "/usr/bin/gpg")
 (compress 0 1 2 3)
 (digestname . "MD5;SHA1;RIPEMD160;SHA256;SHA384;SHA512;SHA224")
 (digest 1 2 3 8 9 10 11)
 (ciphername . 
"IDEA;3DES;CAST5;BLOWFISH;AES;AES192;AES256;TWOFISH;CAMELLIA128;CAMELLIA192;CAMELLIA256")
 (cipher 1 2 3 4 7 8 9 10 11 12 13)
 (pubkey 1 2 3 16 17)
 (version . "1.4.23"))
 
Modifying version-regexp-alist variable resolves the issue.

;; I don't know meaning of "-unknown" version, so I don't know whether
;; "-4" is apropriate value.
(progn (add-to-list 'version-regexp-alist
                    '("^[-._+ ]?unknown$" . -4))
       (epg-find-configuration 'OpenPGP t))
-> ((program . "/usr/bin/gpg2")
 (curve . "cv25519;ed25519;nistp256;nistp384;nistp521;secp256k1")
 (compressname . "Uncompressed;ZIP;ZLIB;BZIP2")
 (compress 0 1 2 3)
 (digestname . "SHA1;RIPEMD160;SHA256;SHA384;SHA512;SHA224")
 (digest 2 3 8 9 10 11)
 (ciphername . 
"IDEA;3DES;CAST5;BLOWFISH;AES;AES192;AES256;TWOFISH;CAMELLIA128;CAMELLIA192;CAMELLIA256")
 (cipher 1 2 3 4 7 8 9 10 11 12 13)
 (pubkeyname . "RSA;ELG;DSA;ECDH;ECDSA;EDDSA")
 (pubkey 1 16 17 18 19 22)
 (version . "2.2.15-unknown"))

-- 
Kazuhiri Ito