perf/tests improvements:

Developer stuff.

. Emit more precise message for missing glibc static library,
  from Arnaldo Carvalho de Melo.

. Show the 'make -f tests/make' inner make output when an error happens.

  The perf build tests harness, invoked with:

    make -C tools/perf -f tests/make

  Will call many combinations of builds, trying to check if all of them
  continue to work over time, for instance, if removing perl support, or
  if building using static libraries still builds fine.

  But one would have to check the contents of a per build test entry
  file to figure out what the error was about. Do it automatically,
  speeding up the process of, for instance, installing missing static
  libraries.

  from Arnaldo Carvalho de Melo.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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