Definitely spend the effort to create a simple makefile.
The "installation" of FANN that you refer in your last message will not
be transfered to your gumstix (and please correct me if i am wrong) as
the buildroot tree does not simply get copied across to the gumstix
image. However the installation has probably produced the libraries for
the gumstix CPU architecture.
The "shortest path to glory" is to use a standard compile line exactly
as the one you mention in your last message along with the parameter -l
followed immediately by an absolute path of your FANN libraries compiled
In general i would certainly advise to invest some time into getting a
simple makefile created for your project. With this you can have global
variables where the paths of the libraries will be stored. According to
the target, make can choose the correct libraries to link with your project.
A very good starting point for a make tutorial is this:
Additionally there are a lot of "quick and dirty" make tutorials all
over the internet. Try googling for "gnu make tutorial" or "make tutorial".
Hope this helps