add %.c->%.i and %.c->%.s rules

The Linux kernel has some helper rules which allow you to quickly produce
some of the intermediary files from C source.  Specifically, you can
create .i files which is the preprocessed output and you can create .s
files which is the assembler output.  This is useful when you are trying
to track down header/macro expansion errors or inline assembly errors.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

config.mk

@@ -214,5 +214,9 @@ $(obj)%.o:	%.S
 	$(CC)  $(AFLAGS) $(AFLAGS_$(@F)) $(AFLAGS_$(BCURDIR)) -o $@ $< -c
 $(obj)%.o:	%.c
 	$(CC)  $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c
+$(obj)%.i:	%.c
+	$(CPP) $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c
+$(obj)%.s:	%.c
+	$(CC)  $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c -S
 
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