allow boards to customize compiler options on a per-file/dir basis

With our Blackfin boards, we like to build the compression routines with
-O2 as our tests show a pretty good size/speed tradeoff.  For the rest of
U-Boot though, we want to stick with the default -Os as that is mostly
control code.  So in our case, we would add a line like so to the board
specific config.mk file:
	CFLAGS_lib_generic += -O2

Now all files under lib_generic/ will have -O2 appended to their build.
Signed-off-by: NMike Frysinger <vapier@gentoo.org>
Acked-by: NJean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

config.mk

@@ -206,11 +206,13 @@ export	TEXT_BASE PLATFORM_CPPFLAGS PLATFORM_RELFLAGS CPPFLAGS CFLAGS AFLAGS
 
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+# Allow boards to use custom optimize flags on a per dir/file basis
+BCURDIR := $(notdir $(CURDIR))
 $(obj)%.s:	%.S
-	$(CPP) $(AFLAGS) -o $@ $<
+	$(CPP) $(AFLAGS) $(AFLAGS_$(@F)) $(AFLAGS_$(BCURDIR)) -o $@ $<
 $(obj)%.o:	%.S
-	$(CC) $(AFLAGS) -c -o $@ $<
+	$(CC)  $(AFLAGS) $(AFLAGS_$(@F)) $(AFLAGS_$(BCURDIR)) -o $@ $< -c
 $(obj)%.o:	%.c
-	$(CC) $(CFLAGS) -c -o $@ $<
+	$(CC)  $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c
 
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