perf record: Add record.build-id config option

Post processing at 'perf record' takes a long time on big machines.

What it does is to find the build-id of binaries found in the event
stream, so that it can make sure, at 'report' time, that the symtabs (be
it ELF, kallsyms, etc) being used to resolve symbols are the ones
matching the binaries found at 'record' time.

Sometimes we just want to skip this processing of events at the end of
the session to get quicker results, making sure the binaries haven't
changed from 'record' to 'report' time.

Add a new config option to control this behavior.

The record.build-id config variable can have one of the following
values:

 - cache: post-process data and save/update the binaries into the
          build-id cache (in ~/.debug).  This is the default.
 - no-cache: post-process the data but not update the build-id cache.
             Same effect as using the -N option.
 - skip: skip post-processing and do not update the cache.
         Same effect as using the -B option.

Reported-and-Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Taeung Song <treeze.taeung@gmail.com>
Link: http://lkml.kernel.org/r/1450144196-22957-1-git-send-email-namhyung@kernel.org
[ Added some more text to the documentation ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>