<div id="comment:0"></div> These header file locations (for use in Cython dependencies only) are currently hardcoded as living in `SAGE_INC`, which is no longer true. This is a step toward #29711, and also preparation for #29847 because it removes use of `sage.env.SAGE_INC`. Depends on #29702 CC: @orlitzky @kliem @kiwifb @dimpase @jhpalmieri Component: **build** Author: **Matthias Koeppe** Branch/Commit: **[`18aae7f`](https://github.com/sagemath/sagetrac-mirror/commit/18aae7f8874d6e05d925ebec99ccbe4585f18683)** Reviewer: **François Bissey, Jonathan Kliem** _Issue created by migration from https://trac.sagemath.org/ticket/29855_