[S] Change in flashrom[main]: Makefile,meson.build: Add support for Sphinx 3.x

[Anastasia Klimchuk (Code Review)]

Attention is currently required from: Anton Samsonov, Thomas Heijligen.

Anastasia Klimchuk has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/77778?usp=email )

Change subject: Makefile,meson.build: Add support for Sphinx 3.x
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Patch Set 3:

(4 comments)

Commit Message:

https://review.coreboot.org/c/flashrom/+/77778/comment/6a9d3d8c_aadecc76 :
PS3, Line 7: 3
3 or 4? From the patch it seems like 4.x is a big change, not 3?

https://review.coreboot.org/c/flashrom/+/77778/comment/eebda22c_e977d6ff :
PS3, Line 10: 7996 and 9217
This is very useful info, but you would need to add full links to GitHub issues (so that it's easier for reviewers to follow), thank you!

https://review.coreboot.org/c/flashrom/+/77778/comment/9404d46a_8056d70c :
PS3, Line 13: but not on `sphinx-build` own level
            : upon which `meson` build relies
I don't fully understand this last part of the sentence, what does it mean "not on sphinx-build own level"?

Patchset:

PS3: 
Anton sorry for such a long delay, I want to try get to this patch soon. I added few small questions, but I will do a deep dive later. Thank you for the patch!