[S] Change in coreboot[main]: genbuild_h: Fix and harden major/minor version parsing

[Nico Huber (Code Review)]

Attention is currently required from: Martin L Roth, Maximilian Brune.

Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/81290?usp=email )

Change subject: genbuild_h: Fix and harden major/minor version parsing
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Patch Set 1:

(2 comments)

File util/genbuild_h/genbuild_h.sh:

https://review.coreboot.org/c/coreboot/+/81290/comment/38f42c7f_07e92d8a :
PS1, Line 39: MAJOR_VER="$(echo "${VERSION}" | sed -n 's/^0*([0-9]*).0*([0-9]*).*/\1/p')"
            : 	MINOR_VER="$(echo "${VERSION}" | sed -n 's/^0*([0-9]*).0*([0-9]*).*/\2/p')"
> we could gain some readability if we used extended regex `sed -E` and removed the `` from the chara […]

Would that be posix conform?

https://review.coreboot.org/c/coreboot/+/81290/comment/4aa3eeed_bd2cec01 :
PS1, Line 40: *
> nit: we could be more explicit and write {2} instead of * (for year and for month)

Can you give an example? I wouldn't be sure how to do that and handle leading
zeros. Also, would that work with other version formats that people might use
locally? (see commit that added the comment and `if` that I removed)