Description of problem:
Package python-mplcairo fails to build from source in Fedora rawhide.

gcc -pthread -Wno-unused-result -Wsign-compare -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DNDEBUG -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -D_GNU_SOURCE -fPIC -fwrapv -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -D_GNU_SOURCE -fPIC -fwrapv -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -D_GNU_SOURCE -fPIC -fwrapv -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -fPIC -Ibuild/include -I/usr/include/pybind11 -I/usr/include/pybind11 -I/usr/lib64/python3.8/site-packages/cairo/include -I/usr/include/python3.8 -c src/_unity_build.cpp -o build/temp.linux-x86_64-3.8/src/_unity_build.o -std=c++1z -fvisibility=hidden -flto -Wall -Wextra -Wpedantic -I/usr/include/cairo -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/libpng16
*** 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 /usr/include/pybind11/attr.h:13,
                 from /usr/include/pybind11/pybind11.h:44,
                 from src/_util.h:8,
                 from src/_mplcairo.h:3,
                 from src/_mplcairo.cpp:1,
                 from src/_unity_build.cpp:2:
/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)
      |     ^~~~~~~~~~~~~~~
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://bugzilla.redhat.com/bugzilla> for instructions.
Preprocessed source stored into /tmp/ccbaWrLW.out file, please attach this to your bugreport.

Version-Release number of selected component (if applicable):
0.2-1.fc32

Steps to Reproduce:
koji build --scratch f32 python-mplcairo-0.2-1.fc32.src.rpm

Additional info:
This package is tracked by Koschei. See:
https://koschei.fedoraproject.org/package/python-mplcairo

This blocks the Python 3.9 rebuild.