So that we do less visual searching on the 'make build-test' output to
see the feature related variables:

After:

  $ make -C tools/perf build-test
  <SNIP>
           make_no_newt_O: cd . && make NO_NEWT=1 FEATURES_DUMP=/home/acme/git/linux/tools/perf/BUILD_TEST_FEATURE_DUMP O=/tmp/tmp.dz55IX DESTDIR=/tmp/tmp.X29xxo
              make_tags_O: cd . && make tags FEATURES_DUMP=/home/acme/git/linux/tools/perf/BUILD_TEST_FEATURE_DUMP O=/tmp/tmp.6ecLh8 DESTDIR=/tmp/tmp.6vIla578Ho
  make_util_pmu_bison_o_O: cd . && make util/pmu-bison.o FEATURES_DUMP=/home/acme/git/linux/tools/perf/BUILD_TEST_FEATURE_DUMP O=/tmp/tmp.SVPM2G DESTDIR=/tmp/tmp.C0oAam

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-dx4krgzqa566v1pedrbrcchi@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>