Include file paths (-I ...)

[Geert Janssens]

While working on the preferences migration I had to introduce two source files that are 
generated during compilation.

These files are generated in the build directory (if building out-of-tree). Without any changes to 
the include paths in the makefiles, this results in a build error (source not found).

I looked a bit closer and found that we are specifying the include search paths as absolut paths 
from the $(top_srcdir), like
-I$(top_srcdir)/src/gnome-utils, ...

Obviously with such a path spec my built source files in the build directory never get found.

If I change the above to
-I../gnome-utils
(this example is for in the gnome/Makefile.am), it works. That is because the compiler will 
expand this path in both the source dir as the build dir.

So my question: is that the right approach and secondly, why was the $(top_srcdir) notation 
chosen in the first place ?

Note that there were already built sources in the gnucash code. These are included using a 
path relative to src, for example
#include "core-utils/gnc-version.h"
and the relevant Makefile.am has a pathspec like
-I$(top_builddir)/src

Seems ... inconsistent ? Or what am I missing ?

Geert