kbuild: filter-out PHONY targets from "targets"

The variable "targets" contains object paths for which existing .*.cmd
files should be included.

scripts/Makefile.build automatically adds $(MAKECMDGOALS) to "targets"
as follows:

  targets += $(extra-y) $(MAKECMDGOALS) $(always)

The $(MAKECMDGOALS) is a PHONY target in several places.  PHONY targets
never create .*.cmd files.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.build

@@ -562,7 +562,7 @@ $(multi-used-m): FORCE
 $(call multi_depend, $(multi-used-m), .o, -objs -y -m)
 
 targets += $(multi-used-y) $(multi-used-m)
-
+targets := $(filter-out $(PHONY), $(targets))
 
 # Descending
 # ---------------------------------------------------------------------------