perf build: Don't unconditionally link the libbfd feature test to -liberty and -lz

perf build: Don't unconditionally link the libbfd feature test to -liberty and -lz

Current libbfd feature test unconditionally links against -liberty and -lz.
While it's required on some systems (e.g. opensuse), it's completely
unnecessary on the others, where only -lbdf is sufficient (debian).
This patch streamlines (and renames) the following feature checks:

feature-libbfd           - only link against -lbfd (debian),
                           see commit 4fdbab48a4de ("perf tools: Fix bfd
			   dependency libraries detection")
feature-libbfd-liberty   - link against -lbfd and -liberty
feature-libbfd-liberty-z - link against -lbfd, -liberty and -lz (opensuse),
                           see commit 30d317b5cf9c ("perf tools: fix BFD
			   detection on opensuse")

(feature-liberty{,-z} were renamed to feature-libbfd-liberty{,z}
for clarity)

The main motivation is to fix this feature test for bpftool which is
currently broken on debian (libbfd feature shows OFF, but we still
unconditionally link against -lbfd and it works).

Tested on debian with only -lbfd installed (without -liberty); I'd
appreciate if somebody on the other systems can test this new detection
method.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/4dfc634cfcfb236883971b5107cf3c28ec8a31be.1542328222.git.sdf@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>