When perf_event_attr.mmap_data is set the kernel will generate
PERF_RECORD_MMAP events when non-exec (data, SysV mem) mmaps are
created, so we need to synthesize from /proc/pid/maps for existing
threads, as we do for exec mmaps.

Right now just 'perf record' does it, but any other tool that uses
perf_event__synthesize_thread(s|map) can request it.
Reported-by: Don Zickus <dzickus@redhat.com>
Tested-by: Don Zickus <dzickus@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Bill Gray <bgray@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Joe Mario <jmario@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Fowles <rfowles@redhat.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-ihwzraikx23ian9txinogvv2@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>