kbuild: fix a bug in regeneration of linker scripts

In some use cases, SPL linker script was not updated even when
it should be.

For instance,

  $ make tricoder_config all
    [ build complete ]
  ... modify include/configs/tricoder.h
  $ make

spl/u-boot-spl.lds should be updated in this case, but it wasn't.

To fix this problem, linker scripts generation should be handled
by $(call if_changed_dep,...) rather than by $(call if_changed,...).

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Reported-by: Andreas Bießmann <andreas.devel@googlemail.com>
Tested-by: Andreas Bießmann <andreas.devel@googlemail.com>

Makefile

@@ -1053,11 +1053,11 @@ depend dep:
 
 # ---------------------------------------------------------------------------
 quiet_cmd_cpp_lds = LDS     $@
-cmd_cpp_lds = $(CPP) $(cpp_flags) $(LDPPFLAGS) -ansi -D__ASSEMBLY__ \
-		-x assembler-with-cpp -P -o $@ $<
+cmd_cpp_lds = $(CPP) -Wp,-MD,$(depfile) $(cpp_flags) $(LDPPFLAGS) -ansi \
+		-D__ASSEMBLY__ -x assembler-with-cpp -P -o $@ $<
 
 u-boot.lds: $(LDSCRIPT) prepare FORCE
-	$(call if_changed,cpp_lds)
+	$(call if_changed_dep,cpp_lds)
 
 PHONY += nand_spl
 nand_spl: prepare

spl/Makefile

@@ -231,11 +231,11 @@ $(u-boot-spl-dirs):
 	$(Q)$(MAKE) $(build)=$@
 
 quiet_cmd_cpp_lds = LDS     $@
-cmd_cpp_lds = $(CPP) $(cpp_flags) $(LDPPFLAGS) -ansi -D__ASSEMBLY__ \
-		-x assembler-with-cpp -P -o $@ $<
+cmd_cpp_lds = $(CPP) -Wp,-MD,$(depfile) $(cpp_flags) $(LDPPFLAGS) -ansi \
+		-D__ASSEMBLY__ -x assembler-with-cpp -P -o $@ $<
 
 $(obj)/u-boot-spl.lds: $(LDSCRIPT) FORCE
-	$(call if_changed,cpp_lds)
+	$(call if_changed_dep,cpp_lds)
 
 # read all saved command lines