gnupg: add patch to fix compilation on device

When running mkdefsinc we get:

  FORTIFY: %n not allowed on Android
  Aborted

packages/gnupg/mkdefsinc.c.patch.ondevice

@@ -0,0 +1,13 @@
+--- ./doc/mkdefsinc.c.orig	2021-09-01 10:39:31.217492425 +0200
++++ ./doc/mkdefsinc.c	2021-09-01 10:41:07.165492356 +0200
+@@ -290,8 +290,8 @@
+         }
+       n = strlen (opt_date) + strlen (month) + 2 + 1;
+       p = xmalloc (n);
+-      snprintf (p, n, "%d %n%s %d",
+-                atoi (opt_date+8), &monthoff, month, atoi (opt_date));
++      snprintf (p, n, "%d %s %d",
++                atoi (opt_date+8), month, atoi (opt_date));
+       xfree (opt_date);
+       opt_date = p;
+     }