gpg: Allow building with older libgpg-error.

* g10/mainproc.c (proc_encrypted): Use constant from logging.h
--

Because the log levels are enums I had to change there names in
libgpg-error to avoid clashes.  Master uses the new names but 2.2
needs to stick to the old names.

Fixes-commit: 825909e9cd
Signed-off-by: Werner Koch <wk@gnupg.org>

g10/mainproc.c

@@ -683,7 +683,7 @@ proc_encrypted (CTX c, PACKET *pkt)
            * are rare in practice we print a hint on how to decrypt
            * such messages.  */
           log_string
-            (GPGRT_LOGLVL_INFO,
+            (GPGRT_LOG_INFO,
              _("Hint: If this message was created before the year 2003 it is\n"
                "likely that this message is legitimate.  This is because back\n"
                "then integrity protection was not widely used.\n"));