Use the same llvm's version as crystal-lang package for CI's darwin b…

…uild (crystal-lang#5804)

* Use llvm5 for darwin build in CI

* Force binaries of llvm in PATH

* DRY for the llvm's version crystal-lang's depends on

* Install jq

bin/ci

@@ -84,7 +84,12 @@ prepare_build() {
 
   on_linux docker pull "jhass/crystal-build-$ARCH"
 
-  on_osx brew install llvm crystal-lang
+  on_osx brew install crystal-lang
+
+  # Make sure binaries from llvm are available in PATH
+  on_osx brew install jq
+  on_osx OSX_LLVM_PACKAGE=`brew info --json=v1 crystal-lang | jq '.[].dependencies | .[] | select(startswith("llvm"))'`
+  on_osx brew link --force $OSX_LLVM_PACKAGE
 }
 
 with_build_env() {