perf jit: Move test functionality in to a test

Adds a test for minimal jit_write_elf functionality.

Committer testing:

  # perf test jit
  61: Test jit_write_elf                                    : Ok
  #

  # perf test -v jit
  61: Test jit_write_elf                                    :
  --- start ---
  test child forked, pid 10460
  Writing jit code to: /tmp/perf-test-KqxURR
  test child finished with 0
  ---- end ----
  Test jit_write_elf: Ok
  #

Committer notes:

Fix up the case where HAVE_JITDUMP is no defined.

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexios Zavras <alexios.zavras@intel.com>
Cc: Allison Randal <allison@lohutok.net>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lore.kernel.org/lkml/20191126235913.41855-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>