Run boot & configure via stack exec.

See #110. [skip ci]

.appveyor.yml

@@ -8,17 +8,18 @@ install:
     - curl -ostack.zip -LsS --insecure https://www.stackage.org/stack/windows-x86_64
     - 7z x stack.zip stack.exe
     - bash -lc "curl -LsS http://www.haskell.org/ghc/dist/7.10.3/ghc-7.10.3-x86_64-unknown-mingw32.tar.xz | tar -xJ -C /mingw64 --strip-components=1"
-    - stack exec -- pacman -S --noconfirm gcc binutils p7zip git
+    - stack exec -- pacman -S --noconfirm perl gcc binutils p7zip git
     - echo "" | stack --no-terminal install alex happy shake ansi-terminal mtl
     - git clone --recursive git://git.haskell.org/ghc.git C:\msys64\home\ghc\tmp
     - bash -lc "mv /home/ghc/tmp/* /home/ghc"
-    - stack exec -- mk/get-win32-tarballs.sh download x86_64
+    - cd C:\msys64\home\ghc
+    - stack exec -- perl boot
+    - stack exec -- configure --enable-tarballs-autodownload
     - ghc   --version
     - stack --version
     - alex  --version
     - happy --version
 
 build_script:
-    - bash -lc "./boot"
-    - bash -lc "echo \"\" | ./configure"
+    - cd
     - bash -lc "./shake-build/build.bat -j --no-progress"