Caused by an explicit rule in Rules.make overriding the default rule
%.o: %.c. The default dependency must be added to the explicit rule.
diff -u linux-2.1.32/Rules.make linux/Rules.make
--- linux-2.1.32/Rules.make Sun Apr 6 12:52:06 1997
+++ linux/Rules.make Sun Apr 13 21:51:10 1997
@@ -194,7 +194,7 @@
endif # CONFIG_MODVERSIONS
ifneq "$(strip $(SYMTAB_OBJS))" ""
-$(SYMTAB_OBJS): $(TOPDIR)/include/linux/modversions.h
+$(SYMTAB_OBJS): $(TOPDIR)/include/linux/modversions.h $(SYMTAB_OBJS:.o=.c)
$(CC) $(CFLAGS) -DEXPORT_SYMTAB -c $(@:.o=.c)
endif