Adding a new target?

[david.hagood at gmail.com]

I am doing cross-compilation of RPMs for an embedded ARM, and what I'd
like to do is add the needed macros such that

rpmbuild -ba <my spec file>.spec -target <my target arch>

But from what I can see, the logic to define a new -target is only in the
/usr/lib directory, and I'd like to be able to reference a more "local" rc
file - ideally, one in the project's directory.

Any suggestions on best practices?