Make <sys/timerfd.h> standalone.

There's no uapi timerfd.h.

Bug: 11559337
Change-Id: I77a4b1365fdcf2c9f18673b11341a165e54b4bbd
diff --git a/libc/include/sys/timerfd.h b/libc/include/sys/timerfd.h
index 0651f1c..1aa97b4 100644
--- a/libc/include/sys/timerfd.h
+++ b/libc/include/sys/timerfd.h
@@ -29,12 +29,18 @@
 #ifndef _SYS_TIMERFD_H_
 #define _SYS_TIMERFD_H_
 
+#include <fcntl.h> /* For O_CLOEXEC and O_NONBLOCK. */
 #include <time.h>
 #include <sys/types.h>
-#include <linux/timerfd.h>
 
 __BEGIN_DECLS
 
+#define TFD_TIMER_ABSTIME (1 << 0)
+#define TFD_TIMER_CANCEL_ON_SET (1 << 1)
+
+#define TFD_CLOEXEC O_CLOEXEC
+#define TFD_NONBLOCK O_NONBLOCK
+
 extern int timerfd_create(clockid_t, int);
 extern int timerfd_settime(int, int, const struct itimerspec*,
                            struct itimerspec*);