boost/math/tools/config.hpp: Cherry pick boostorg/math #729

[mkoeppe]

Cherry-picked the header file change from boostorg/math#729

Fixes scipy/scipy#15296

Ref: https://trac.sagemath.org/ticket/33080

[mckib2]

Thanks @mkoeppe! I do have a maintenance concern with cherry-picking, see below for potential resolution

@rgommers How do we handle patches with other vendored code? I assume we want a way to replay these changes on any future updates to this repo we make, so we might need to make some additions to make_headers.py to apply a set of patches based on the boost versions. You tell me -- is that complicating things too much or is that the right amount of complication?

[mckib2]

Also just remembered that scipy is not pointing to latest commit -- it's pointing to 2110ce2. Let's do a real fix -- I'll do the following:

• "revert" this repo to have its latest commit point at Boost 1.75 headers
• add in machinery to apply patches bases on target Boost versions

Then you'll be able to generate a patch file to be applied rather than manually tracking what has been cherry-picked

[rgommers]

That sounds like a good idea. We typically have patch files to go with the vendored libraries, for example:

• scipy/sparse/linalg/dsolve/SuperLU/scipychanges.patch
• scipy/scipy/sparse/linalg/eigen/arpack/ARPACK/README.scipy

[mckib2]

@mkoeppe I think with #6, we're ready to have you generate a patch file and place it in the patches/ directory. After that is completed, we'll then need an accompanying PR against SciPy to update the submodule commit

[mckib2]

Thanks @mkoeppe, this side LGTM! Thanks for helping us work through this