@vbraun - this is needed for the current develop with Flint 3

This is based on the branch of #36677 rebased over current develop

upstream_url seems broken - https://github.com/sagemath/sage/actions/runs/7154743273/job/19482626735#step:14:89

probably the usual GH "autotarball" blues - upstream hadn't provided their own release tarball 😞

./configure: line 44875: SAGE_SPKG_CONFIGURE_ARB: command not found
-----------------------------------------------------------------------------
Checking whether SageMath should install SPKG symengine...
checking whether any of gmp arb ecm flint mpc mpfr is installed as or will be installed as SPKG... yes; install symengine as well
configure: no suitable system package found for SPKG symengine

https://github.com/sagemath/sage/actions/runs/7188248886/job/19577575728?pr=36847#step:11:949

good catch. This must be the issue

Documentation preview for this PR (built with commit 798f546; changes) is ready! 🎉

Looking good.
The failures in Build&Test (https://github.com/sagemath/sage/actions/runs/7215897580/job/19661231248?pr=36847#step:17:19985) are unrelated.
The failure in https://github.com/sagemath/sage/actions/runs/7215897597/job/19661265123?pr=36847#step:11:10584 is random failure #36832