perf trace: Fix the selection for architectures to generate the errno name tables

Make the architecture test directory agree with the code comment.

Committer notes:

This was split from a larger patch.

The code was assuming the developer always worked from tools/perf/, so make sure we
do the test -d having $toolsdir/perf/arch/$arch, to match the intent expressed in the comment,
just above that loop.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexios Zavras <alexios.zavras@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Igor Lubashev <ilubashe@akamai.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wei Li <liwei391@huawei.com>
Link: http://lore.kernel.org/lkml/20200306071110.130202-4-irogers@google.com


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