perf probe: Fix build when DWARF support libraries not present
perf probe: Fix build when DWARF support libraries not present

On a freshly installed system, after libelf-dev is installed we get:

    CC       /tmp/build/perf/util/probe-event.o
  util/probe-event.c: In function ‘try_to_find_probe_trace_events’:
  util/probe-event.c:753:46: error: unused parameter ‘target’ [-Werror=unused-parameter]
       int max_tevs __maybe_unused, const char *target)
                                                ^
    CC       /tmp/build/perf/util/cgroup.o
  util/probe-event.c: At top level:
  util/probe-event.c:193:12: error: ‘get_text_start_address’ defined but not used [-Werror=unused-function]
   static int get_text_start_address(const char *exec, unsigned long *address)
            ^
  cc1: all warnings being treated as errors
  make[1]: *** [/tmp/build/perf/util/probe-event.o] Error 1
  make[1]: *** Waiting for unfinished jobs....
  make: *** [install] Error 2

Fix it by enclosing functions only used when those libraries are installed
under the suitable preprocessor define and using __maybe_unused to a function
that is only built when DWARF support is disabled.

Problem introduced in this changeset:

  commit fb7345bbf7fad9bf72ef63a19c707970b9685812
  Author: Masami Hiramatsu <60fcdccfd958d359debfe6e6e7417cd7f1aaa9e3@hitachi.com>
  Date:   Thu Dec 26 05:41:53 2013 +0000

      perf probe: Support basic dwarf-based operations on uprobe events

Cc: Adrian Hunter <41bb5944f244750b7cf0394140496972a3f1bee3@intel.com>
Cc: David Ahern <b80c1600f604d3b0d768f26f90a76757e76005dd@gmail.com>
Cc: Frederic Weisbecker <e8a1bf9163cb25e93cfd6540f223b3872ea7ee55@gmail.com>
Cc: Jiri Olsa <2c6594f608aa3d41e98d48846a6328831f7084ad@redhat.com>
Cc: Masami Hiramatsu <60fcdccfd958d359debfe6e6e7417cd7f1aaa9e3@hitachi.com>
Cc: Mike Galbraith <3cfa3897b7f55b5396b7a47c83b66325184bc9b4@gmx.de>
Cc: Namhyung Kim <5c915a589b3ddf58cebf14bec41bcc143b37ac3c@kernel.org>
Cc: Paul Mackerras <19a0ba370c443ba08d20b5061586430ab449ee8c@samba.org>
Cc: Peter Zijlstra <3fddac958924aef220f202ca567388ddab3f14a8@infradead.org>
Cc: Stephane Eranian <f199ae9781930a5b94b284ca2f471140752002a7@google.com>
Link: 06baa0213c41d6e358926555c8f450f461a8c7cf@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <293abb6b76d7791c0732cc517d38c4b5c734b87f@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs