Improve top-level recursive Makefile
Improve top-level recursive Makefile

Previously if a build failed in a subdirectory, the process would
continue with the next, sometimes making it difficult to see that there
were build errors in one part of the project. The updated Makefile
corrects that.

Lluiso/oor,Lluiso/oor,OpenOverlayRouter/oor,OpenOverlayRouter/oor,OpenOverlayRouter/oor,Lluiso/oor,Lluiso/oor,OpenOverlayRouter/oor,OpenOverlayRouter/oor,OpenOverlayRouter/oor,Lluiso/oor,OpenOverlayRouter/oor