sims/nic/corundum,net/menshen: add ENABLE_VERILATOR option

Disabled by default as verilator is a bit tricky with versions etc.

sims/net/menshen/rules.mk

@@ -52,5 +52,7 @@ $(bin_menshen): $(verilator_bin_menshen)
 	cp $< $@
 
 CLEAN := $(bin_menshen) $(verilator_dir_menshen) $(OBJS)
+ifeq ($(ENABLE_VERILATOR),y)
 ALL := $(bin_menshen)
+endif
 include mk/subdir_post.mk

sims/nic/corundum/rules.mk

@@ -55,5 +55,8 @@ $(bin_corundum): $(verilator_bin_corundum)
 	cp $< $@
 
 CLEAN := $(bin_corundum) $(verilator_dir_corundum) $(OBJS)
+
+ifeq ($(ENABLE_VERILATOR),y)
 ALL := $(bin_corundum)
+endif
 include mk/subdir_post.mk