SConstruct: Place toplevel include symlinks in core/build/include
SConstruct: Place toplevel include symlinks in core/build/include

This is friendlier than core/../build/include, which breaks if core is
built standalone.

omco/geode,omco/geode,mikest/geode,omco/geode,mikest/geode,mikest/geode,mikest/geode,omco/geode