[build:Makefile] Ensure compatibility with BSD make

[bashonly]

BSD Make can't do $(shell ...). We were already using it in the MARKDOWN and SYSCONFDIR vars, but by using it in CODE_FOLDERS and CODE_FILES I broke the yt-dlp target for bmake.

Also:

• immediately raise error if GNU Make <4 is being used
• include fixes for the yt-dlp target if bmake is run in jobs mode
• remove vestigial SYSCONFDIR var assignment
• exclude __pyinstaller subdir from tarball

GNU Make versions older than 4.0 don't support !=, but considering that gmake 4.0 was released in 2013 IMO we shouldn't need to support it. Apparently Debian was holding onto make 3.8x for a while, but as of Jessie it was bumped to 4.0 (and all Debian versions up-to-and-including Jessie ship EOL Python anyways). CentOS 7 still has make 3.8x, but it is EOL as of the end of June.

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

[Grub4K]

Makefiles are great 👍

[pukkandan]

Why? User should be able to run pyinstaller from source tar

[bashonly]

it was, fixed in 43cfd46