[M] Change in coreboot[main]: Makefile.mk: Use one line per *_common flag

[Maximilian Brune (Code Review)]

Attention is currently required from: Elyes Haouas, Felix Singer, Martin L Roth.

Maximilian Brune has posted comments on this change by Felix Singer. ( https://review.coreboot.org/c/coreboot/+/83226?usp=email )

Change subject: Makefile.mk: Use one line per *_common flag
......................................................................

Patch Set 1:

(1 comment)

Patchset:

PS1:
> By the paste, I've sorted CFLAGS by kind and alphabetically (https://review.coreboot. […]

I would prefer that to be a separate commit, since it is easier for review.
Now I can easily see that no option has been forgotten, since the order is the same.
And in the separate commit I just have to see that no more lines were added than removed (or vice versa) to see that it is good to go.