1. NOTE: These instructions use ~/.local/llvm_$(opam config var switch) as an install root for llvm/clang, but installing elsewhere should be fine. Also note that you probably don't want to use this clang for anything else because it is a default debug build and hence very slow. So some PATH management is likely needed to have ~/.local/llvm_$(opam config var switch) in PATH only when building / running llair. This is done automatically for the targets in test/Makefile.
2. clone llvm, clang, and libcxxabi
   - cd ~/path/to/sledge
   - git clone git+ssh://git@github.com/jberdine/llvm.git --branch ocaml_api
   - git clone https://github.com/llvm-mirror/clang.git llvm/tools/clang
   - git clone https://github.com/llvm-mirror/libcxxabi.git llvm/projects/libcxxabi
3. build llvm & clang
   - brew install cmake ninja
   - cd ~/path/to/sledge/llvm
   - mkdir _build
   - cd _build
   - cmake -G Ninja -DCMAKE_INSTALL_PREFIX=~/.local/llvm_$(opam config var switch) -DLLVM_OCAML_INSTALL_PATH=~/.local/llvm_$(opam config var switch)/lib/ocaml ..
   - ninja -j8
   - ninja ocaml_doc
   - ninja install
4. install deps
   - add ~/.local/llvm_$(opam config var switch)/bin to shell PATH
     + because installing the opam package for llvm will look for it
     + export PATH=~/.local/llvm_$(opam config var switch)/bin:$PATH
   - pin conf-llvm
     + opam pin add -n conf-llvm --dev
     + opam pin edit conf-llvm
       - edit version number to match that of the llvm clone (= 7.0.0)
   - pin llvm
     + cd ~/path/to/sledge/llvm
     + opam pin add -n -k git llvm .
     + opam pin edit llvm
       - edit llvm and conf-llvm version number to match that of the llvm clone (= 7.0.0)
       - when prompted, ok to save new opam file
5. hush `ld: warning: directory not found for option '-L/opt/local/lib'`
   - the zarith package adds a spurious linker option unless you have both brew and macports, so if you see this linker warning when compiling, execute
     + sudo mkdir -p /opt/local/lib
6. install dev tools
   - opam install merlin ocp-indent tuareg user-setup
   - install ocamlformat
7. if needed: point new clang to xcode c++ lib
   - cd ~/.local/llvm_$(opam config var switch)/include
   - ln -s /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++ .
8. llvm dev workflow
   - modify llvm sources
   - cd ~/path/to/sledge/llvm/_build; ninja -j8
   - iterate
   - (optional?) git add -u; git commit -m ...
   - ninja -j8 && ninja ocaml_doc && ninja install && opam upgrade llvm
   - cd ~/path/to/sledge; make
   - it is not uncommon to get "inconsistent assumptions" errors: clean and re-make
9. llvm emacs mode
   - (add-to-list 'load-path (expand-file-name "~/path/to/sledge/llvm/utils/emacs"))
   - (require 'llvm-mode)
   - (require 'autodisass-llvm-bitcode)