Add CircleCI script (#364)

circle.yml

+machine:
+  xcode:
+    version: 8.0
+  environment:
+    MODE: --flavour=quickest --integer-simple
+
+dependencies:
+  override:
+    - brew update
+    - brew install ghc cabal-install
+    - cabal update
+    - cabal install alex happy ansi-terminal mtl shake quickcheck
+  cache_directories:
+    - $HOME/.cabal
+    - $HOME/.ghc
+
+compile:
+  override:
+    # Fetch GHC sources into ./ghc
+    - git --version
+    - git config --global url."git://github.com/ghc/packages-".insteadOf git://github.com/ghc/packages/
+    - git clone --depth 1 --recursive git://github.com/ghc/ghc
+
+    - mkdir ghc/hadrian
+    # move hadrian's .git into ./ghc/hadrian and perform a hard reset in order to regenerate Hadrian files
+    - mv .git ghc/hadrian
+    # NOTE: we must write them in the same line because each line
+    # in CircleCI is a separate process, thus you can't "cd" for the other lines
+    - cd ghc/hadrian; git reset --hard HEAD
+
+    # XXX: export PATH doesn't work well either, so we use inline env
+    # Self test
+    - PATH=$HOME/.cabal/bin:$PATH ghc/hadrian/build.sh selftest
+
+    # Build GHC
+    - PATH=$HOME/.cabal/bin:$PATH ghc/hadrian/build.sh -j $MODE --verbose --no-progress --progress-colour=never --progress-info=brief --profile=-
+
+test:
+  override:
+    # Test GHC binary
+    - ghc/inplace/bin/ghc-stage2 -e 1+2