bug#68996: [PATCH] Respect warnings added in GNU Make 4.4.90

[Eli Zaretskii <eliz@gnu.org>]

> From: Collin Funk <collinfunk38@gmail.com>
> Date: Thu, 08 Feb 2024 19:00:02 -0800
> 
> When building Emacs with recent versions of GNU Make every object file
> built will result in a warning like so:
> 
> ../src/verbose.mk:58: warning: invalid variable reference ' '
>   CC       emacs-module.o

Why did Make have to break Makefiles that depend on this "feature"?

> This doesn't prevent Emacs from building but makes it slightly harder
> to see any build output. I attached a patch that should work for all
> versions of GNU Make, both before and after the change. However it
> also causes the indentation to disappear in-front of CC and ELC which
> looks a bit strange. It doesn't seem like there is a valid way to do
> this at the moment. More discussion about this change can be seen
> here: https://savannah.gnu.org/bugs/?65273
> 
> Feel free to change my patch if you see a better way to solve these
> warnings.

My vote is for GNU Make to support this feature, since there's no good
way of having it otherwise (given what Paul Smith says in that
discussion).  Adding Paul Eggert in case he has ideas.  Paul, how do
other project produce the same indented "CC foo.o"? do they also use
this trick? or something else?

> Also, I have never committed to Emacs. This change feels trivial but
> results in 34 lines changed. Therefore I was unsure if this patch
> could be Copyright-paperwork-exempt tagged. Feel free to email me off
> list if I must fill them out. Thanks

Let's see if we want to install this.  I'm not sure.