perf jevents: Make build fail on JSON parse error

Today, when a JSON file fails parsing the build continues, but there are
no json files built in, which is difficult to debug later.  Make the
build stop on a parse error instead.

v2: Add fixes from Sukadev. Now we handle architectures
    with no JSON events correctly. And fix some stale comments.

Committer note:

Tested by running the cross build container tests, that were all failing
for v1.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20170725001638.19990-1-andi@firstfloor.org


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