Use GHC 8.8 as the minimum bootstrap compiler version

This patch makes GHC 8.8 the minimum bootstrap compiler across all Docker images in preparation for the same requirement being imposed on GHC. In most cases, I was able to use 8.8.3. The exception is x86_64-linux-deb10, where the only 8.8 bindist I could find was 8.8.1.

Note that I was unable to install cabal-install-3.0.0.0 on x86_64-linux-alpine, even after lots of struggled attempts to do so. As a result, I have settled for cabal-install-2.4.1.0 on that distro. This probably isn't the worst thing in the world, given that x86_64-linux-deb10 also combines GHC 8.8 with cabal-install-2.4.1.0.

aarch64-linux-deb9/Dockerfile

@@ -26,8 +26,7 @@ RUN curl http://releases.llvm.org/$BOOT_LLVM_VERSION/clang+llvm-$BOOT_LLVM_VERSI
     $BOOT_LLVM_DIR/bin/llc --version
 
 # GHC
-# Use 8.8.1 to bootstrap, since earlier releases are especially buggy on AArch64
-ENV GHC_VERSION 8.8.1
+ENV GHC_VERSION 8.8.3
 RUN curl http://downloads.haskell.org/~ghc/$GHC_VERSION/ghc-$GHC_VERSION-aarch64-deb9-linux.tar.xz | tar -xJ
 WORKDIR /ghc-$GHC_VERSION
 RUN ./configure --prefix=/usr/local LLC=$BOOT_LLVM_DIR/bin/llc OPT=$BOOT_LLVM_DIR/bin/opt && \