tools/perf/build: Pass through LDFLAGS to feature tests

David Ahern reported that when passing in LDFLAGS=-static then
the feature checks still succeed - causing build failures down
the line because the static libraries are missing.

Solve this by passing through LDFLAGS to the feature-check
Makefile.

Reported-by: David Ahern <dsahern@gmail.com>
Tested-by: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20131007155129.GA1066@gmail.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>