tools/perf/build: Split out feature checks: 'liberty', 'liberty-z', 'cplus-demangle'

Note that these are rarely executed tests, so we call feature_check() explicitly
and don't have them in CORE_FEATURE_CHECKS.

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/n/tip-pvumlx6mbtfxffgrlwO2mRcx@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>