Extract fcntl to <bits/fcntl.h>.

Bug: http://b/28067717
Change-Id: Id8c19056244660a6e0276a5614282af8d41fbe1e
diff --git a/libc/include/fcntl.h b/libc/include/fcntl.h
index 9d15e92..5967903 100644
--- a/libc/include/fcntl.h
+++ b/libc/include/fcntl.h
@@ -36,6 +36,8 @@
 #include <linux/stat.h>
 #include <linux/uio.h>
 
+#include <bits/fcntl.h>
+
 #if defined(__USE_GNU) || defined(__USE_BSD)
 #include <bits/lockf.h>
 #endif
@@ -63,7 +65,6 @@
 
 extern int creat(const char*, mode_t);
 extern int creat64(const char*, mode_t);
-extern int fcntl(int, int, ...);
 extern int openat(int, const char*, int, ...);
 extern int openat64(int, const char*, int, ...);
 extern int open(const char*, int, ...);