So we need to trow away just stdout, leaving stderr to be caught by
the build tests infrastructure, so that we can see what went wrong
when the tarpkg build test fails:

  $ make -C tools/perf build-test
  make: Entering directory '/home/acme/git/linux/tools/perf'
  - tarpkg: ./tests/perf-targz-src-pkg .
  tests/make:302: recipe for target 'tarpkg' failed
  make[1]: *** [tarpkg] Error 2
  Makefile:102: recipe for target 'build-test' failed
  make: *** [build-test] Error 2
  make: Leaving directory '/home/acme/git/linux/tools/perf'
  $ cat tools/perf/tarpkg
  ./tests/perf-targz-src-pkg .
    PERF_VERSION = 4.5.g05f5ec
    PERF_VERSION = 4.5.g05f5ec
  In file included from bench/mem-memcpy-x86-64-asm.S:9:0:
  bench/../../../arch/x86/lib/memcpy_64.S:5:29: fatal error: asm/cpufeatures.h: No such file or directory
  compilation terminated.
  mv: cannot stat ‘bench/.mem-memcpy-x86-64-asm.o.tmp’: No such file or directory
  make[5]: *** [bench/mem-memcpy-x86-64-asm.o] Error 1
  make[5]: *** Waiting for unfinished jobs....
  make[4]: *** [bench] Error 2
  make[4]: *** Waiting for unfinished jobs....
  make[3]: *** [perf-in.o] Error 2
  make[3]: *** Waiting for unfinished jobs....
  make[2]: *** [all] Error 2
  $

So the test flow is:

1. Run: 'make -C tools/perf build-test'

2. One of its tests failed, in this case, the 'tarpkg' one

3. Look at what went wrong, by looking at the output of that test, in
   tools/perf/tarpkg

Admittedly, this should be shortcircuited to showing what went wrong directly
from the 'make build-test' step, but lets first fix this tarpkg one and the
problem it spotted, which should be fixed by adding some extra file to the
tools/perf/MANIFEST so that detached tarballs continue being self contained and
build successfully.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ynld6egoxolmftcddpnd7oh6@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>