I don't think that using pathconf is an important part of this issue. Instead, it is more important to deal with ENAMETOOLONG errors. To do so, we should get rid of all stack allocations of arrays with PATH_MAX/MAXPATHLEN size (also because they can consume quite a lot of stack).

I agree that it important to scope this issue. You need to determine whether you want it to be a bug fix or a cleanup action. If the issue is "fails to build on HP-UX", then all other aspects not relevant to this issue need to be left out, in particular the introduction of new symbolic constants.

If the objective is the code clean-up, all versions but 3.4 need to be left out.

IOW, -1 on systematic introduction of PY_PATH_MAX to 2.7, 3.2, and 3.3.