I've been reading about Developing a Library Module, from which I learned that
If your library module is written in another language, you can compile it with Clang.
If I follow those instructions using the Clang supplied by Apple's XCode Command-Line Tools (Apple LLVM version 10.0.1 (clang-1001.0.46.4) Target: x86_64-apple-darwin18.7.0), my composition won't run, and I find the following error in the Console:
loadModule():1763 Error: Couldn't parse module 'my.test_lib.bc': Unknown bitstream version!.
As far as I can tell by inspecting the LLVM source code, this is about the MODULE_CODE_VERSION record in the bitcode file. But according to the historical documentation, the last time a new bitstream version was introduced was between LLVM 4.0.1 and LLVM 5.0.
I can't find any command-line switches to tell Clang to emit earlier versions of bitcode, which is unsurprising because LLVM documentation does warn that bitcode is not intended to be used as a storage format or expected to be compatible between compiler releases.
Is vuo-compile really still based on a Clang/LLVM from 2017? What's the best way to discover which version it was built with?