tools/perf/build: Fix detection of non-core features

tools/perf/build: Fix detection of non-core features

feature_check needs to be invoked through call, and LDFLAGS may not be
set so quotes are needed.

Thanks to Jiri for spotting the quotes around LDFLAGS; that one was
driving me nuts with the upcoming timerfd feature detection.

Signed-off-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Jiri Olsa <jolsa@redhat.com>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1383064996-20933-1-git-send-email-dsahern@gmail.com
[ Fixed conflict with 8a0c4c2843d3 ("perf tools: Fix libunwind build and feature detection for 32-bit build") ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>