perf tools: Fix bfd dependency libraries detection

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 <[email protected]>
Tested-by: Ingo Molnar <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Corey Ashford <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Jiri Olsa <[email protected]>