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

[Eli Zaretskii]

> From: David Engster <deng@randomsample.de>
> Date: Thu, 16 May 2013 21:09:38 +0200
> 
> When doing parallel builds using GNU Make, jumping to the location of a
> warning/error from the compilation buffer often does not work. This is
> because GNU Make enters different directories at the same time, and the
> resulting output is intermixed. The attached patch fixes this by looking
> at all directories which were entered up to the point of the
> warning/error, instead of just taking the directly preceding one. I'm
> aware that this is not a perfect solution, since those directories might
> contain files with identical names, in which case Emacs might show the
> wrong one, but IMO it's still an improvement over the current
> situation. This feature can also be disabled through a new variable.

I think this problem should be fixed in GNU Make.  And, lo and behold,
the next release of GNU Make will have a switch that will prevent the
directories from being mixed.  Perhaps it would be better to teach
compile.el to detect support for that switch (-O or --output-sync) and
use it if available when -j is also used, than to kludge around the
current behavior.