tools lib traceevent: Fix strerror_r() use in pevent_strerror

glibc-2.16 starts to mark the function with attribute warn_unused_result
so that it can cause a build warning.

Since GNU version of strerror_r() can return a pointer to a string
without setting @buf, check the return value and copy/truncate it to our
buffer if needed.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1345618831-9148-5-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>