Remove dependencies on obsolete __ARCH_WANT_SYSCALL_NO_FLAGS syscalls.

(aarch64 kernels only have the newer system calls.)

Also expose the new functionality that's exposed by glibc in our header files.

Change-Id: I45d2d168a03f88723d1f7fbf634701006a4843c5

libc/include/sys/eventfd.h

@@ -25,6 +25,7 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+
 #ifndef _SYS_EVENTFD_H
 #define _SYS_EVENTFD_H