allow for differing RIOT* paths

Makefile.include

@@ -101,7 +101,7 @@ debug:
 	$(DEBUGGER) $(DEBUGGER_FLAGS)
 
 buildtest:
-	@for BOARD in $$(sed -n -e 's/ifeq[^,]*,\([^)]*\))/\1/p' $(RIOTBASE)/boards/Makefile.base); do \
+	@for BOARD in $$(sed -n -e 's/ifeq[^,]*,\([^)]*\))/\1/p' $(RIOTBOARD)/Makefile.base); do \
 		echo -n "Building for $${BOARD} .. "; \
-		env -i PATH=$${PATH} BOARD=$${BOARD} $(MAKE) -B clean all >/dev/null 2>&1 && echo "success" || echo "failed"  ; \
+		env -i PATH=$${PATH} BOARD=$${BOARD} RIOTBASE=$${RIOTBASE} RIOTBOARD=$${RIOTBOARD} RIOTCPU=$${RIOTCPU} $(MAKE) -B clean all >/dev/null 2>&1 && echo "success" || echo "failed"  ; \
 	done