Update docs for generating unoptimized debug builds

[WillAyd]

Not sure what changes were made recently to the compilers package but I've noticed without undef'ing _FORTIFY_SOURCES that the compiler throws a lot of errors about having that defined with optimizations turned off. Looks like we were also missing flags for C++

I forget where the original conversation was about this, but I'm assuming these flags are never going away with the compilers package. @rgommers does NumPy still use that package or have you moved on to a possibly better solution?

[rgommers]

The compilers package is still relevant, and we're using it in NumPy, SciPy and various other places. There is no good alternative yet unfortunately.

I haven't seen this problem yet. Could you add the errors you're seeing and the version/platform of compilers where you started seeing this in a comment or PR description?

[WillAyd]

Ah OK - I think I am starting to see the warning as I'm experimenting with some C++ extensions, and the warning seems to come from C++ not C

  /home/willayd/miniforge3/envs/pandas-dev/x86_64-conda-linux-gnu/sysroot/usr/include/features.h:330:4: warning: #warning _FORTIFY_SOURCE requires compiling with optimization (-O) [-Wcpp]
    330 | #  warning _FORTIFY_SOURCE requires compiling with optimization (-O)

I'll have to do some more research to pinpoint the versions and exact conditions under which this appears, but I'm seeing it on ubuntu 24.04. Looks like the compilers package installs gcc=13.3.0=h9576a4e_1