Bug#1096535: dolfinx-mpc: ftbfs with GCC-15

[Drew Parsons]

Source: dolfinx-mpc
Followup-For: Bug #1096535
Control: tags -1 ftbfs

Upstream has run a battery of tests.

Looks like gcc-15 is not a problem itself.

The problem might not be the nanobind version either (sometimes
nanobind upgrades will give an ABI conflict, but 2.5 is supposed to be
be compatible with 2.4).

Rather, the problem seems to be the way nanobind weaves gcc into the
object files it needs.

So the conflict comes from one package (basix, or dolfinx) using
nanobind with gcc-14, and another package (dolfinx-mpc) trying to
build via nanobind with gcc-15.

The libraries will work together once they are all built with the same
gcc.

(To be on the safe side, it's probably helpful not to change the
nanobind version in the middle of a gcc transition, too).

In other words, when we have major gcc updates, all nanobind clients
need to be rebuilt with the same gcc.

In the FEniCS suite, the nanobind clients are basix, dolfinx,
dolfinx_mpc and scifem.