Fix #5871 For AArch64, use Debian 10 rather than Ubuntu 20.04

Author: mpilgrem

etc/dockerfiles/arm64.Dockerfile

@@ -1,8 +1,12 @@
-FROM ubuntu:20.04
+# Stack is built with GHC 9.2.4. GHC 9.2.4 for Linux/AArch64 says it was made on
+# a Debian 10 system and requires GMP 6.1. Debian 10 is codename 'buster' and
+# includes libc6 (2.28-10+deb10u1).
+FROM debian:buster
 
 RUN DEBIAN_FRONTEND=noninteractive apt-get update && apt-get install -y \
-    curl build-essential curl libffi-dev libffi7 libgmp-dev libgmp10 libncurses-dev libncurses5 libtinfo5 libnuma-dev xz-utils \
-    g++ gcc libc6-dev libffi-dev libgmp-dev make zlib1g-dev git gnupg netbase
+    curl build-essential curl libffi-dev libffi7 libgmp-dev libgmp10 \
+    libncurses-dev libncurses5 libtinfo5 libnuma-dev xz-utils g++ gcc \
+    libc6-dev libffi-dev libgmp-dev make zlib1g-dev git gnupg netbase
 
 RUN cd /tmp && \
     curl -L https://github.com/llvm/llvm-project/releases/download/llvmorg-9.0.1/clang+llvm-9.0.1-aarch64-linux-gnu.tar.xz --output /tmp/llvm.tar.xz && \