x86_64-linux-alpine: Try GHC 8.6.5

x86_64-linux-alpine/Dockerfile

-FROM alpine:3.9
+FROM alpine:3.10.2
 
 RUN echo "Installing GHC build dependencies..." && \
     apk add --no-cache \
         autoconf=~2.69 \
         automake=~1.16 \
-        binutils-gold=~2.31 \
+        binutils-gold=~2.32 \
         build-base=~0.5 \
-        coreutils=~8.30 \
+        coreutils=~8.31 \
         cpio=~2.12 \
-        ghc=~8.4 \
-        linux-headers=~4.18 \
+        linux-headers=~4.19 \
         libffi-dev=~3.2 \
         musl-dev=~1 \
         ncurses-dev=~6.1 \
-        python3=~3.6 \
+        python3=~3.7 \
         py3-sphinx=~1.8 \
         zlib-dev=~1.2 \
         xz=~5.2 \
-        bash=~4.4 \
-        git=~2.20 \
+        bash=~5.0 \
+        git=~2.22 \
         wget=~1.20 \
         sudo=~1.8 \
         grep=~3 \
-        cabal=~2.2
+        curl=~7.66 \
+        gmp-dev=~6.1 \
+        cabal=~2.4
+
+WORKDIR /tmp
+# Install GHC
+ENV GHC_VERSION 8.6.5
+# NB: This is not an official bindist, but rather an alternative bindist taken
+#     from https://github.com/redneb/ghc-alt-libc.
+RUN curl -L https://github.com/redneb/ghc-alt-libc/releases/download/ghc-$GHC_VERSION-musl/ghc-$GHC_VERSION-x86_64-unknown-linux-musl.tar.xz | tar -Jx;
+WORKDIR /tmp/ghc-$GHC_VERSION
+RUN ./configure --disable-ld-override --prefix=/opt/ghc/$GHC_VERSION; \
+    make install;
+
+WORKDIR /tmp
+RUN rm -rf /tmp/ghc-$GHC_VERSION
+ENV PATH /opt/ghc/$GHC_VERSION/bin:$PATH
 
 # Create a normal user.
 RUN adduser ghc --gecos "GHC builds" --disabled-password
@@ -31,8 +46,8 @@ USER ghc
 WORKDIR /home/ghc/
 
 # Build Haskell tools
-RUN cabal update && \
-    cabal install hscolour happy alex --constraint 'happy ^>= 1.19.10'
+RUN cabal v2-update && \
+    cabal v2-install hscolour happy alex --constraint 'happy ^>= 1.19.10'
 ENV PATH /home/ghc/.cabal/bin:$PATH
 ENV SPHINXBUILD /usr/bin/sphinx-build-3