gh-37161: Fix cvxopt build with suitesparse homebrew; fixes #37149.
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This PR tries to fix issue #37149.
The problem is that cvxopt doesn't build correctly when using the
homebrew-provided version of SuiteSparse.
As suggested in the discussion of the issue, I added the
`CVXOPT_SUITESPARSE_INC_DIR` environment variable in the `.homebrew-
build-env` file.
This is an ugly workaround, and should probably be reported/discussed
also on the cvxopt repo, since the issue seems to be that they do
`#include "umfpack.h"` instead of a more proper `#include
"suitesparse/umfpack.h"`.
Indeed, for Linux system, their `setup.py` script then has to set the
include folder to be `whatever/include/suitesparse` instead of the
default system one.
Also, I don't have a way to check if this breaks other installations.
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### :hourglass: Dependencies
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URL: https://github.com/sagemath/sage/pull/37161
Reported by: Riccardo Zanotto
Reviewer(s): John H. Palmieri
