6648 illumos build should be explicit about C standards

@@ -63,11 +63,11 @@
 gen_layout_obj.o := CFLAGS += $(CTF_FLAGS)
 gen_layout_obj.o := CFLAGS64 += $(CTF_FLAGS)
 gen_layout_obj.o := POST_PROCESS_O = $(CTFCONVERT_O)
 
 gen_struct_layout:      ../common/gen_struct_layout.c
-                $(NATIVECC) $(NATIVECC_CFLAGS) -o $@ \
+                $(NATIVECC) $(NATIVE_CFLAGS) -o $@ \
                         ../common/gen_struct_layout.c -lctf
 
 clean:
                 $(RM) $(OBJS) $(CLEANFILES) gen_struct_layout \
                   check_struct_layout gen_layout_obj.o \