contrib: use automatic mirror resolver for ftp.gnu.org

Refs #74834

Change-Id: I398420100a5419ea19b5800b076cbcdad13261a1

contrib/src/main.mak

@@ -21,7 +21,7 @@ DATE := $(shell date +%Y%m%d)
 VPATH := $(TARBALLS)
 
 # Common download locations
-GNU := http://ftp.gnu.org/gnu
+GNU := http://ftpmirror.gnu.org/
 SF := http://heanet.dl.sourceforge.net/sourceforge
 CONTRIB_VIDEOLAN ?= http://downloads.videolan.org/pub/contrib
 GNUTELEPHONY := https://github.com/dyfet

contrib/src/nettle/rules.mak

 # Nettle
 
 NETTLE_VERSION := 3.1
-NETTLE_URL := ftp://ftp.gnu.org/gnu/nettle/nettle-$(NETTLE_VERSION).tar.gz
+NETTLE_URL := $(GNU)/nettle/nettle-$(NETTLE_VERSION).tar.gz
 
 ifeq ($(call need_pkg,"nettle >= 3.1"),)
 PKGS_FOUND += nettle