Adding new test that process metrics code and checks the expected
results. Starting with easy ipc metric.

Committer testing:

  # perf test "Parse and process metrics"
  67: Parse and process metrics                             : Ok
  #
  # perf test -v "Parse and process metrics"
  67: Parse and process metrics                             :
  --- start ---
  test child forked, pid 103402
  metric expr inst_retired.any / cpu_clk_unhalted.thread for IPC
  found event inst_retired.any
  found event cpu_clk_unhalted.thread
  adding {inst_retired.any,cpu_clk_unhalted.thread}:W
  test child finished with 0
  ---- end ----
  Parse and process metrics: Ok
  #

Had to fix it to initialize that 'struct value' array sentinel with a
named initializer to fix the build with some versions of clang:

  tests/parse-metric.c:135:7: error: missing field 'val' initializer [-Werror,-Wmissing-field-initializers]
                { 0 },
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200602214741.1218986-13-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>