Separate ghc install dir for each matrix run

Author: jneira

.azure/windows-stack.yml

@@ -43,7 +43,8 @@ jobs:
       curl -sSkL http://www.stackage.org/stack/windows-x86_64 -o /usr/bin/stack.zip
       unzip -o /usr/bin/stack.zip -d /usr/bin/
       mkdir -p "$STACK_ROOT"
-      echo "local-programs-path: D:/bin/stack" > "$STACK_ROOT/config.yaml"
+      GHC_VERSION=${YAML_FILE:6:5}
+      echo "local-programs-path: D:/bin/stack-$GHC_VERSION" > "$STACK_ROOT/config.yaml"
     displayName: Install stack
   - bash: |
       source .azure/windows-stack.bashrc