build.jl runs at install time on users’ machines. For your own maintenance
purposes you could manually enable the BuildProcess provider when you know
you have a compiler available, but maintainers don’t need Julia to run
things just for building C++ binaries.
We’re going to separate the tooling in a better way long term so
maintainers have better templates and build environments set up for
producing binaries across platforms, and the install time build script that
runs on users’ systems only has to download a platform-dependent file.
If you plan on also building a conda package via conda-forge anyway, you
could make use of their infrastructure. I haven’t been entirely sold on
using conda-forge as a general solution for Julia packages that aren’t
Python bindings for a few reasons I won’t get into right now, but if you
can make it work, go for it.