macOS CI: Upgrade GNU make in ci/cirrusci.sh

This should fix Phobos CI, which expects such prerequisites provisioning
to happen in DMD's ci/cirrusci.sh. Because this YAML addition hasn't been
duplicated in Phobos, Phobos CI is still using the default make on macOS,
which is too old and doesn't support the newly required `private` modifier.

.github/workflows/main.yml

@@ -115,11 +115,6 @@ jobs:
         uses: dlang-community/setup-dlang@v1.3.0
         with:
           compiler: ${{ matrix.host_dmd }}
-      - name: 'MacOS: Install recent make'
-        if: runner.os == 'macOS'
-        run: |
-          brew install make
-          echo "PATH=/usr/local/opt/make/libexec/gnubin:$PATH" >> $GITHUB_ENV
 
       - name: Set up repos
         run: |

ci/cirrusci.sh

@@ -27,6 +27,11 @@ if [ "$OS_NAME" == "linux" ]; then
   fi
   apt-get -q update
   apt-get install -yq $packages
+elif [ "$OS_NAME" == "osx" ]; then
+  # update GNU make
+  brew install make
+  rm /usr/bin/make
+  ln -s /usr/local/opt/make/libexec/gnubin/make /usr/bin/make
 elif [ "$OS_NAME" == "freebsd" ]; then
   packages="git gmake devel/llvm12"
   if [ "$HOST_DMD" == "dmd-2.079.0" ] ; then