Account for distutils being deprecated and python3.10 becoming default on Ubuntu 22.04

[Patol75]

Closes #346

I am opening this PR as a draft; it will be needed in the future given changes in the Python distribution. Please feel free to contribute, as it is likely I will succeed in figuring everything out.

I have tried to identify instances where distutils is used and replace them with equivalent logic from either setuptools or sysconfig.

Something of potential interest is setuptools indicating that the setup.py approach is deprecated. Instead, pyproject.toml and setup.cfg files should be used, in combination with the build and pip packages. I have tried to build the fluidity package this way.

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Judging from Actions, Focal is successful, but Bionic does not find a valid version of Python.

[Patol75]

I think this is starting to head in the right direction. I am giving it a CI test to see if the new python_build behaves.

@stephankramer

• Could you let me know what the aclocal.m4 files are and what they do? I have modified them to mirror the changes in the configure files, but it is not clear to me what this actually does.
• To account for the deprecated setup.py approach and the new recommended build + pip strategy, I have removed default and fltools from the install target in Makefile.in. The main reason is that pip should not be run as root (I still do it in the clean target, but I guess this is more acceptable). Considering default and fltools do not require root privileges, but install does, I am not sure if it made sense to have them in. Additionally, an improvement from the new pip logic is that PYTHONPATH does not need to be set anymore to access fluidity's python modules.
• Some C++ files in tools were apparently missing the unistd.h header inclusion. I am not quite sure how chdir was executed before.

[gnikit]

@Patol75 you might want to have a look at https://github.com/nektos/act . I use it for local Actions testing. Maybe you can use it with only a couple failing tests, on a single docker container and get some info on the errors.

Also, I am not sure if this is relevant but HAVE_NUMPY if true, is never actually #defined in confdefs.h like the rest of our preprocessor macros, so that might lead to some cryptic failures.

[Patol75]

Thanks for the suggestion. I tried, but I did not manage to get a successful build, unfortunately. I thought that fluidity being in the sudo group was the reason that Python could not find installed libraries, but apparently not.

Locally, if I run ./configure --enable-2d-adaptivity CPPFLAGS=-I/usr/local/include && make makefiles && sudo make clean && make -j && make -j fltools, followed by tools/testharness.py -f top_hat_cv.xml, I get Passes. Python libraries are properly installed at /home/thomas/.local/lib/python3.8/site-packages, and that is where they are imported from.

[Patol75]

I am closing this PR as I will likely open a new one based on the deprecate_distutils_2 branch.