Setting TBB_ROOT to the out path is necessary as otherwise the bundled
FindTBB.cmake tries to search the `tbb.dev` output for the library
files.
Note that embree and nanoflann are bundled within the source. The build
system is not currently setup to use non-vendored libs.
Rebuilt 25 times to test reproducibility.
Attempted a build on x86_64-darwin, and it failed, so marking this as
linux only.
