To build the toolchain, you need a recent C++ toolchain supporting C++17:
MSVC 2017 or newer
Clang 6.0.0 or newer
GCC 7.3.0 or newer Stable operation of older toolchains is not guaranteed. You also need zlib 1.2.3.4 or newer. Python 2.7 is required to run tests. Optionally, you can use ninja-build. For more info about LLVM software requirements visit: https://llvm.org/docs/GettingStarted.html.