tools build feature: Introduce feature_assign macro

The feature_assign macro generates feature value
assignment for name, like:

  $(call feature_assign,dwarf) == feature-dwarf=1

This will be used more in following patches.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Wang Nan <wangnan0@huawei.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama <pi3orama@163.com>
Link: http://lkml.kernel.org/r/1450893514-9158-4-git-send-email-jolsa@kernel.org
[ Rename it to feature_assign, the original shorter name was misleading, to say the least ;-) ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/Makefile.feature

@@ -122,8 +122,14 @@ define feature_print_text_code
     MSG = $(shell printf '...%30s: %s' $(1) $(2))
 endef
 
+#
+# generates feature value assignment for name, like:
+#   $(call feature_assign,dwarf) == feature-dwarf=1
+#
+feature_assign = feature-$(1)=$(feature-$(1))
+
 FEATURE_DUMP_FILENAME = $(OUTPUT)FEATURE-DUMP$(FEATURE_USER)
-FEATURE_DUMP := $(foreach feat,$(FEATURE_DISPLAY),feature-$(feat)($(feature-$(feat))))
+FEATURE_DUMP := $(foreach feat,$(FEATURE_DISPLAY),$(call feature_assign,$(feat)))
 FEATURE_DUMP_FILE := $(shell touch $(FEATURE_DUMP_FILENAME); cat $(FEATURE_DUMP_FILENAME))
 
 # The $(feature_display) controls the default detection message