perf dlfilters: Fix build on environments with a --sysroot gcc arg

perf dlfilters: Fix build on environments with a --sysroot gcc arg

Such as cross building on Android, so just add EXTRA_CFLAGS to the
dlfilters rules as it is where --sysroot= has been specified.

Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lore.kernel.org/lkml/YS1JwIMTNNWcbGdT@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>