Working around Centos 8 failure.

[rwgk]

Using -DCMAKE_BUILD_TYPE=Debug for Centos 8 as a work around for the failure below.

The failure was first observed around 2020-06-04, when the gcc version changed from 8.3 to 8.4:

2359.txt: gcc-c++                  x86_64  8.3.1-5.1.el8                          appstream   12 M
2360.txt: gcc-c++                  x86_64  8.4.1-1.el8                            appstream   12 M

# cmake --build build --target pytest
Consolidate compiler generated dependencies of target cross_module_gil_utils
[  4%] Built target cross_module_gil_utils
Consolidate compiler generated dependencies of target pybind11_cross_module_tests
[  9%] Built target pybind11_cross_module_tests
Consolidate compiler generated dependencies of target pybind11_tests
[100%] Built target pybind11_tests
gmake[3]: *** [tests/CMakeFiles/pytest.dir/build.make:72: tests/CMakeFiles/pytest] Segmentation fault (core dumped)
gmake[2]: *** [CMakeFiles/Makefile2:249: tests/CMakeFiles/pytest.dir/all] Error 2
gmake[1]: *** [CMakeFiles/Makefile2:256: tests/CMakeFiles/pytest.dir/rule] Error 2
gmake: *** [Makefile:183: pytest] Error 2

For future reference, to reproduce the crash in a docker container (thanks @henryiii):

docker run --rm --cap-add=SYS_PTRACE --security-opt seccomp=unconfined -it centos:8 /bin/bash
yum update -y && yum install -y python3-devel gcc-c++ gdb make git && python3 -m pip install --upgrade pip && git clone https://github.com/pybind/pybind11.git && cd pybind11 && python3 -m pip install cmake -r tests/requirements.txt --prefer-binary && cmake -S . -B build -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -DDOWNLOAD_EIGEN=ON -DCMAKE_CXX_STANDARD=11 -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") && cmake --build build -j 16
cd build/tests
python3 -c "import pybind11_tests" # Crashes