Precompiled LLVM 9.0.0 Windows binaries

The Windows binaries available on llvm.org are useless to build Faust's LLVM backend, so we keep our own precompiled binaries here. This isn't the very latest LLVM version, but tried and tested and known to work with the Faust version that we use.

Note that the 64 bit package is straight from Pierre Guillot's upstream, while the 32 bit binaries (needed for building the external for 32 bit versions of Pd and Purr Data) are our own. These are primarily intended for our AppVeyor builds, they may or may not work for you when trying to build pd-faustgen2 on Windows, use at your own risk. :)