Download the GCC sources insecurely

This is needed as they are built on a long-outdated Debian version. :(

src/ci/docker/host-x86_64/dist-x86_64-linux/build-gcc.sh

@@ -22,7 +22,8 @@ cd gcc-$GCC
 # latter host is presented to `wget`! Therefore, we choose to download from the insecure HTTP server
 # instead here.
 #
-sed -i'' 's|ftp://gcc\.gnu\.org/|https://gcc.gnu.org/|g' ./contrib/download_prerequisites
+# FIXME: use HTTPS (see https://github.com/rust-lang/rust/pull/86586#issuecomment-868355356)
+sed -i'' 's|ftp://gcc\.gnu\.org/|http://gcc.gnu.org/|g' ./contrib/download_prerequisites
 
 ./contrib/download_prerequisites
 mkdir ../gcc-build