perf symbols: Fallback to kallsyms when using the minimal 'ELF' loader

perf symbols: Fallback to kallsyms when using the minimal 'ELF' loader

The minimal ELF loader should not return 1 when it manages to read the
vmlinux build-id, it should instead return 0, meaning that it hasn't
loaded any symbols, since it doesn't parses ELF at all.

That way, the main symbol.c routines will understand that it is
necessary to continue looking for a file with symbols, and when no
libelf is linked, that means it will eventually try kallsyms.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Tested-by: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
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: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20141111130326.GT18464@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>