It seems we have a circular dependency issue with build preventing bootstrapping a pep517 toolchain if using the latest version of tomli.

I'm seeing the following dependency cycles here preventing me from using the latest tomli with build:

build -> pep517 -> tomli -> build(needed for building pep517 packages like tomli)
build -> tomli -> build(needed for building pep517 packages like tomli)

I think the solution is to probably have both pep517 and build vendor tomli, although maybe only pep517 needs to vendor it.