Makfile: move suffix rules to Makefile.build

This commit moves suffix rules from config.mk
to scripts/Makefile.build, which will allow us
to switch smoothly to real Kbuild.

Note1:
post/lib_powerpc/fpu/Makefile has
its own rule to compile C sources.
We need to tweak it to keep the same behavior.

Note2:
There are two file2 with the same name:
arch/arm/lib/crt0.S and eamples/api/crt0.S.
To keep the same build behavior,
examples/api/Makefile also has to be treaked.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/examples/api/Makefile b/examples/api/Makefile
index f770859..52f4368 100644
--- a/examples/api/Makefile
+++ b/examples/api/Makefile
@@ -50,9 +50,9 @@
 		$(OBJCOPY) -O binary $< $@ 2>/dev/null
 
 # Rule to build generic library C files
-$(obj)%.o: $(SRCTREE)/lib/%.c
+$(addprefix $(obj),$(notdir $(EXT_COBJ_FILES-y))): $(obj)%.o: $(SRCTREE)/lib/%.c
 	$(CC) -g $(CFLAGS) -c -o $@ $<
 
 # Rule to build architecture-specific library assembly files
-$(obj)%.o: $(SRCTREE)/arch/$(ARCH)/lib/%.S
+$(addprefix $(obj),$(notdir $(EXT_SOBJ_FILES-y))): $(obj)%.o: $(SRCTREE)/arch/$(ARCH)/lib/%.S
 	$(CC) -g $(CFLAGS) -c -o $@ $<