kqueue1(2): export the symbol from libc

Reviewed by:	emaste, jhb
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D39271

lib/libc/sys/Symbol.map

@@ -419,6 +419,7 @@ FBSD_1.6 {
 FBSD_1.7 {
 	_Fork;
 	fspacectl;
+	kqueue1;
 	swapoff;
 };
 

sys/sys/event.h

@@ -361,6 +361,7 @@ struct timespec;
 
 __BEGIN_DECLS
 int     kqueue(void);
+int     kqueue1(unsigned flags);
 int     kevent(int kq, const struct kevent *changelist, int nchanges,
 	    struct kevent *eventlist, int nevents,
 	    const struct timespec *timeout);