I can access ftp://ftp.gnutls.org/gcrypt/gnutls/v3.5/ that is defined original ./oe-core/meta/recipes-support/gnutls/gnutls.inc and it works to me.
However, if you can’t access the site due to security problem in your company, you can replace to your suggestion (https://gnupg.org/ftp/gcrypt/gnutls).