bug#14411: 24.3.50; compile.el: Better file search for parallel builds

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: David Engster <deng@randomsample.de>,  14411@debbugs.gnu.org
> Date: Fri, 18 Sep 2020 16:35:50 +0200
> 
> On the other hand, David's patch seems to fix this stuff automatically,
> so my preference would be to just drop the defcustom and do the search,
> anyway -- it's only done if we can't find the file name otherwise, so it
> should only help, and never (?) hurt?

I don't mind installing the feature.  But can we just make sure it is
still effective, with modern Make and our current Makefiles?