do not run public headers build test on generated headers
While we can argue if generated files should be tested the issue here is that atm there is a different set of tests running between these two scenarioes
make configure
make
make configure
make test_public_headers_build
vs
make configure
make test_public_headers_build
The continue
in this MR skips files from the build area during globbing (that don't exist in the latter example, but do exist in the former).