perf symbols: Destroy unused symsrcs

Stephane reported that perf report and annotate failed to process data
using lots of (> 500) shared libraries.  It was because of the limit on
number of open files (ulimit -n).

Currently when perf loads a DSO, it'll look for normal and dynamic
symbol tables.  And if it fails to find out both tables, it'll iterate
all of possible symtab types.  But many of them are useless since they
have no additional information and the problem is that it's not closing
those files even though they're not used.  Fix it.
Reported-by: NStephane Eranian <eranian@google.com>
Signed-off-by: NNamhyung Kim <namhyung@kernel.org>
Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1392859976-32760-2-git-send-email-namhyung@kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol.c

@@ -1336,6 +1336,8 @@ int dso__load(struct dso *dso, struct map *map, symbol_filter_t filter)
 
 			if (syms_ss && runtime_ss)
 				break;
+		} else {
+			symsrc__destroy(ss);
 		}
 
 	}