bug#17438: xrandr linking problem on OS X

[Glenn Morris]

Paul Eggert wrote:

>> Does configure.ac really need to require this version of pkg-config, or just 
>> autogen.sh?
>
> If the xrandr configuration is failing due to a bug in older
> pkg-config versions, this suggests that configure.ac really needs the
> newer pkg-config.

But it's not failing in that way in the emacs-24 branch on hydra, which
also uses pkg-config 0.23. So the problem is in pkg.m4 that older
pkg-config supply, not the pkg-config program.

I think it's that they don't do the equivalent of

--exists && --cflags && --libs

https://bugs.freedesktop.org/show_bug.cgi?id=29801

> I suppose we could go back to the emacs-24 way of doing things, and
> use or own PKG_CHECK_MODULES macro.

I think this is equivalent to my suggestion of copying pkg.m4 from a
recent pkg-config into our m4 directory.

But assuming we can get a newer pkg-config on hydra, I think it would be
fine to require >= 0.26 in autogen.sh, and leave configure.ac alone.