Building Saar Raz's clang concepts branch

A Recipe for building Saar Raz's clang concepts branch

Saar Raz has been working on a Concepts implementation, available at https://github.com/saarraz/clang-concepts It's not much harder to build it than clang usually is, it's just a matter of getting things checked out into the right places before configuring the build. Just like LLVM and clang normally. In order to double check how, I peeked at the shell script used by the compiler explorer image to build the clang-concepts compiler: https://github.com/mattgodbolt/compiler-explorer-image/blob/master/clang/build/build-concepts.sh The really important bit is getting exactly the right commit from LLVM, 893a41656b527af1b00a1f9e5c8fcecfff62e4b6. To get a working directory something like: Starting from where you want your working tree and build tree, e.g ~/bld/llvm-concepts 
git clone https://github.com/llvm-mirror/llvm.git

pushd llvm
git reset --hard 893a41656b527af1b00a1f9e5c8fcecfff62e4b6
popd

pushd llvm/tools
git clone https://github.com/saarraz/clang-concepts.git clang
popd

pushd llvm/projects
git clone https://github.com/llvm-mirror/libcxx.git
git clone https://github.com/llvm-mirror/libcxxabi.git
# The sanitizers: this is optional but you want them
git clone https://github.com/llvm-mirror/compiler-rt.git
popd
Then to build and install 
mkdir build && cd build

cmake \
    -DCMAKE_INSTALL_PREFIX=~/install/llvm-concepts/ \
    -DLLVM_ENABLE_LIBCXX=yes  \
    -DCMAKE_BUILD_TYPE=Release  \
    -DLLVM_ENABLE_ASSERTIONS=yes \
    -DLLVM_PARALLEL_LINK_JOBS=1 \
    -G Ninja  \
    ../llvm/

ninja

ninja check

ninja install
Note that I install into a separate prefix, keeping it isolated from everything else. The compiler can be invoked as ~/install/llvm-concepts/bin/clang++. There's no particular reason to put the compiler on your PATH.