perf tools: add NO_BACKTRACE for application self-debugging

perf has support for self-debugging by defining dump_stack function.
This function uses backtrace and backtrace_symbols functions defined as
GNU extensions.

In Android, bionic does not offer support for these functions and
compilation will fail with the following error:

target  C: libperf <= tools/perf/util/util.c
tools/perf/util/util.c:4:22: fatal error: execinfo.h: No such file or directory
compilation terminated.

Add a compile-time option (NO_BACKTRACE) to enable or disable
self-debugging functionality in perf. This can also help in debugging
since it offers the possibility to turn on/off printing the backtrace.

Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1347065004-15306-12-git-send-email-irina.tirdea@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/util.c

@@ -1,7 +1,9 @@
 #include "../perf.h"
 #include "util.h"
 #include <sys/mman.h>
+#ifndef NO_BACKTRACE
 #include <execinfo.h>
+#endif
 #include <stdio.h>
 #include <stdlib.h>
 
@@ -163,6 +165,7 @@ size_t hex_width(u64 v)
 }
 
 /* Obtain a backtrace and print it to stdout. */
+#ifndef NO_BACKTRACE
 void dump_stack(void)
 {
 	void *array[16];
@@ -177,3 +180,6 @@ void dump_stack(void)
 
 	free(strings);
 }
+#else
+void dump_stack(void) {}
+#endif