Change to the NetBSD archive URL rather than the CDN

The CDN has been down for a few hours. Switch to an alternative for the
time being so we can unblock CI.

It appears that the CDN is quite a bit faster, so we will likely want to
switch back when available.

src/ci/docker/host-x86_64/dist-x86_64-netbsd/build-netbsd-toolchain.sh

@@ -27,13 +27,19 @@ mkdir -p /x-tools/x86_64-unknown-netbsd/sysroot
 
 # URL=https://ci-mirrors.rust-lang.org/rustc
 
-SOURCE_URL=https://cdn.netbsd.org/pub/NetBSD/NetBSD-9.0/source/sets
+# FIXME: the archive URL is being used temporarily while the CDN is down.
+# We should serve this from our own CDN
+# SOURCE_URL=https://cdn.netbsd.org/pub/NetBSD/NetBSD-9.0/source/sets
+SOURCE_URL=http://archive.netbsd.org/pub/NetBSD-archive/NetBSD-9.0/source/sets
 curl $SOURCE_URL/src.tgz | tar xzf -
 curl $SOURCE_URL/gnusrc.tgz | tar xzf -
 curl $SOURCE_URL/sharesrc.tgz | tar xzf -
 curl $SOURCE_URL/syssrc.tgz | tar xzf -
 
-BINARY_URL=https://cdn.netbsd.org/pub/NetBSD/NetBSD-9.0/amd64/binary/sets
+# FIXME: the archive URL is being used temporarily while the CDN is down.
+# We should serve this from our own CDN
+# BINARY_URL=https://cdn.netbsd.org/pub/NetBSD/NetBSD-9.0/amd64/binary/sets
+BINARY_URL=http://archive.netbsd.org/pub/NetBSD-archive/NetBSD-9.0/amd64/binary/sets
 curl $BINARY_URL/base.tar.xz | \
   tar xJf - -C /x-tools/x86_64-unknown-netbsd/sysroot ./usr/include ./usr/lib ./lib
 curl $BINARY_URL/comp.tar.xz | \