Use correct CFLAGS in debug mode

[holke]

The configure option --enable-debug sets CFLAGS and CXXFLAGS to -g -O2.

It should set them to -g -Og or -g -O0 instead.

[Davknapp]

In the Cmake build system the optimization level is not specified for debug mode. Therefore this Issue is still relevant.

[spenke91]

I looked into it a little and came to the conclusion that in Cmake it is best practice not to set optimization and debug flags manually, but instead let CMake handle it via the -DCMAKE_BUILD_TYPE. Hence, I think it's not a bug but a feature that we do not specify it in CMake :-)

In our Github workflows, we deviate from this rule by setting -O1 explicitly for debug mode. It does make the github workflows quite a bit faster compared to the default (which uses -O0 "under the hood"). I think this speed up outweighs the cons of deviating from the pure debug case a little here, in particular, considering we cannot run debugger sessions interactively in the github workflow anyway.

I therefore propose to close this issue if nobody objects in the next dev meeting.

[spenke91]

As discussed in the t8code week meeting today, I close this issue because there is nothing to be done.