netgen-mesher fails to build with gcc 10:

[ 23%] Building CXX object libsrc/occ/CMakeFiles/occ.dir/python_occ.cpp.o
make[5]: Leaving directory '/builddir/build/BUILD/netgen-6.2.1810/serial/netgen'
RPM build errors:
*** WARNING *** there are active plugins, do not report this as a bug unless you can reproduce it without enabling any plugins.
Event                            | Plugins
PLUGIN_FINISH_UNIT               | annobin: Generate final annotations
PLUGIN_START_UNIT                | annobin: Generate global annotations
PLUGIN_ALL_PASSES_START          | annobin: Generate per-function annotations
PLUGIN_ALL_PASSES_END            | annobin: Register per-function end symbol
In file included from /usr/include/pybind11/cast.h:13,
                 from /builddir/build/BUILD/netgen-6.2.1810/libsrc/occ/../general/ngpython.hpp:10,
                 from /builddir/build/BUILD/netgen-6.2.1810/libsrc/occ/python_occ.cpp:4:
/usr/include/pybind11/pybind11.h: In constructor 'pybind11::class_<type_, options>::class_(pybind11::handle, bool)':
/usr/include/pybind11/pybind11.h:1058:5: internal compiler error: in nothrow_spec_p, at cp/except.c:1247
 1058 |     PYBIND11_OBJECT(class_, generic_type, PyType_Check)
      |     ^~~~~~~~~~~~~~~

This failure happened during our Python 3.9 rebuilds. While not related to Python 3.9, it still blocks it.

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01176372-netgen-mesher/

For all our attempts to build netgen-mesher with Python 3.9, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.9/package/netgen-mesher/