perf trace beauty open_flags: Add missing headers

Those beautifiers need to make sure they include what they reference,
as changes in builtin-trace.c may end up removing needed stuff, like
when undefining _GNU_SOURCE.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-a9cz8za6lqutfapn5e7uum09@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/trace/beauty/open_flags.c

+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 
 static size_t syscall_arg__scnprintf_open_flags(char *bf, size_t size,
 					       struct syscall_arg *arg)