perf tools: Fix bfd dependency libraries detection

There's false assumption in the library detection code
assuming -liberty and -lz are always present once bfd
is detected. The fails on Ubuntu (14.04) as reported
by Ingo.

Forcing the bdf dependency libraries detection any
time bfd library is detected.

Reported-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Ingo Molnar <mingo@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1398676935-6615-1-git-send-email-jolsa@kernel.org


Signed-off-by: Jiri Olsa <jolsa@kernel.org>