Since this is the name that 'make' will look for if no explicit -f file
is passed.

This in turn makes the output of 'build-test' more compact:

Before:

  $ perf stat make -C tools/perf build-test
  <SNIP>
  cd . && make FEATURE_DUMP_COPY=/home/acme/git/linux/tools/perf/BUILD_TEST_FEATURE_DUMP feature-dump
          make_no_libaudit_O: cd . && make -f Makefile  O=/tmp/tmp.tHIa0Kkk2Y DESTDIR=/tmp/tmp.foK7rckkVi NO_LIBAUDIT=1 FEATURES_DUMP=/home/acme/git/linux/tools/perf/BUILD_TEST_FEATURE_DUMP
  <SNIP>

After:

  $ perf stat make -C tools/perf build-test
  <SNIP>
          make_no_libaudit_O: cd . && make  O=/tmp/tmp.tHIa0Kkk2Y DESTDIR=/tmp/tmp.foK7rckkVi NO_LIBAUDIT=1 FEATURES_DUMP=/home/acme/git/linux/tools/perf/BUILD_TEST_FEATURE_DUMP
  <SNIP>

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-m440lb8dkfsywsyah0htif6t@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>