perf build: Add feature-dump target

To provide FEATURE-DUMP into $(FEATURE_DUMP_COPY) if defined, with no
further action.

Get feature dump of the current build:
  $ make feature-dump
    BUILD:   Doing 'make -j4' parallel build

  Auto-detecting system features:
  ...                         dwarf: [ on  ]

  FEATURE-DUMP file available in FEATURE-DUMP

Get feature dump static build into /tmp/fd file:

  $ make feature-dump FEATURE_DUMP_COPY=/tmp/fd LDFLAGS=-static
    BUILD:   Doing 'make -j4' parallel build

  Auto-detecting system features:
  ...                         dwarf: [ OFF ]

  SNIP

  FEATURE-DUMP file copied into /tmp/fd

Suggested-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1452830421-77757-6-git-send-email-wangnan0@huawei.com
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile.perf

@@ -610,6 +610,17 @@ clean: $(LIBTRACEEVENT)-clean $(LIBAPI)-clean $(LIBBPF)-clean $(LIBSUBCMD)-clean
 	$(QUIET_SUBDIR0)Documentation $(QUIET_SUBDIR1) clean
 	$(python-clean)
 
+#
+# To provide FEATURE-DUMP into $(FEATURE_DUMP_COPY)
+# file if defined, with no further action.
+feature-dump:
+ifdef FEATURE_DUMP_COPY
+	@cp $(OUTPUT)FEATURE-DUMP $(FEATURE_DUMP_COPY)
+	@echo "FEATURE-DUMP file copied into $(FEATURE_DUMP_COPY)"
+else
+	@echo "FEATURE-DUMP file available in $(OUTPUT)FEATURE-DUMP"
+endif
+
 #
 # Trick: if ../../.git does not exist - we are building out of tree for example,
 # then force version regeneration: