As discussed on discord, we have never actually been able to build with the project-wide published min version of 3.14.3. The buildbot that tests the Python configuration is currently pinned to 3.19.1, and there are a number of non-version/policy controlled features that Python building relies on that makes it unreliable with older versions. Some of the issues are pretty fundamental and I don't know how to do them on the older version. I think that, as an optional feature, at least advertising the PSA as in this patch is a good middle ground until the next project-wide CMake version bump.
Also moves setup logic to a macro so that everyone can use it.
CHECK_* directives for message() where added in Cmake 3.17, LLVM
requires 3.14 as minimum so they may not be intepreted correctly and
just print "CHECK_*" into the message stream. Replace them with STATUS.
Reviewed By: stellaraccident
Differential Revision: https://reviews.llvm.org/D91959
* Makes `pip install pybind11` do the right thing with no further config.
* Since we now require a version of pybind11 greater than many LTS OS installs (>=2.6), a more convenient way to get a recent version is preferable.
* Also adds the version spec to find_package so it will skip older versions that may be lying around.
* Tested the full matrix of old system install, no system install, pip install and no pip install.
Differential Revision: https://reviews.llvm.org/D91903
