regressions: Add missing ck_ring SPMC benchmark.

regressions/Makefile

@@ -18,6 +18,7 @@ all:
 	$(MAKE) -C ./ck_stack/validate all
 	$(MAKE) -C ./ck_stack/benchmark all
 	$(MAKE) -C ./ck_ring/validate all
+	$(MAKE) -C ./ck_ring/benchmark all
 	$(MAKE) -C ./ck_rwlock/validate all
 	$(MAKE) -C ./ck_rwlock/benchmark all
 	$(MAKE) -C ./ck_hp/validate all
@@ -41,6 +42,7 @@ clean:
 	$(MAKE) -C ./ck_stack/validate clean
 	$(MAKE) -C ./ck_stack/benchmark clean
 	$(MAKE) -C ./ck_ring/validate clean
+	$(MAKE) -C ./ck_ring/benchmark clean
 	$(MAKE) -C ./ck_rwlock/validate clean
 	$(MAKE) -C ./ck_rwlock/benchmark clean
 	$(MAKE) -C ./ck_hp/validate clean

regressions/ck_ring/benchmark/Makefile

@@ -11,3 +11,4 @@ clean:
 	rm -rf *~ *.o $(OBJECTS) *.dSYM
 
 include ../../../build/regressions.build
+CFLAGS+=-D_GNU_SOURCE