apr include error for macOS 10.12.4

[kybr]

Building a fresh clone of the devel branch* fails with the following error:

/Users/ky/Downloads/********/AlloSystem/allocore/src/io/../private/al_ImplAPR.h:44:11: fatal error:
      'apr-1.0/apr_general.h' file not found
        #include "apr-1.0/apr_general.h"

Here's a commit that exhibits the error:

commit 33560a41c39da286362c315da81cee0ff06a3ea3
Author: Lance Putnam <putnam.lance@gmail.com>
Date:   Thu May 4 13:24:37 2017 +0100

    File: add default ctor and open function with path and mode

Here's a commit that does not exhibit the error:

commit ef6c11c74abfd93d31ecb7e4fc1ea634917a71f0
Author: Karl Yerkes <karl.yerkes@gmail.com>
Date:   Sun Jan 15 09:49:16 2017 -0800

    removing types that break on windows

[grrrwaaa]

I have the same issue here, on OSX 10.11.6. I've gone back through the commits and the problem seems to be produced first by the commit here:
8f718df

Which is pretty bizarre, as that seems to be mostly concerned with AL_WINDOWS!

[grrrwaaa]

The problem was a preprocessor check failing in al_Config.h that I believe was failing because AL_OSX was already defined in a cmake script, and thus al_Config.h was wrongly then defining AL_LINUX. A fix checked in here: 8702eaa