Detect arch4random_addrandom() existence

Refs: libevent#370
Refs: libevent#475

CMakeLists.txt

@@ -338,6 +338,7 @@ CHECK_FUNCTION_EXISTS_EX(sysctl EVENT__HAVE_SYSCTL)
 CHECK_FUNCTION_EXISTS_EX(accept4 EVENT__HAVE_ACCEPT4)
 CHECK_FUNCTION_EXISTS_EX(arc4random EVENT__HAVE_ARC4RANDOM)
 CHECK_FUNCTION_EXISTS_EX(arc4random_buf EVENT__HAVE_ARC4RANDOM_BUF)
+CHECK_FUNCTION_EXISTS_EX(arc4random_addrandom EVENT__HAVE_ARC4RANDOM_ADDRANDOM)
 CHECK_FUNCTION_EXISTS_EX(epoll_create1 EVENT__HAVE_EPOLL_CREATE1)
 CHECK_FUNCTION_EXISTS_EX(getegid EVENT__HAVE_GETEGID)
 CHECK_FUNCTION_EXISTS_EX(geteuid EVENT__HAVE_GETEUID)

configure.ac

@@ -342,6 +342,7 @@ AC_CHECK_FUNCS([ \
   accept4 \
   arc4random \
   arc4random_buf \
+  arc4random_addrandom \
   eventfd \
   epoll_create1 \
   fcntl \

evutil_rand.c

@@ -192,12 +192,14 @@ evutil_secure_rng_get_bytes(void *buf, size_t n)
 	ev_arc4random_buf(buf, n);
 }
 
+#if !defined(EVENT__HAVE_ARC4RANDOM) || defined(EVENT__HAVE_ARC4RANDOM_ADDRANDOM)
 void
 evutil_secure_rng_add_bytes(const char *buf, size_t n)
 {
 	arc4random_addrandom((unsigned char*)buf,
 	    n>(size_t)INT_MAX ? INT_MAX : (int)n);
 }
+#endif
 
 void
 evutil_free_secure_rng_globals_(void)

include/event2/util.h

@@ -842,6 +842,7 @@ int evutil_secure_rng_init(void);
 EVENT2_EXPORT_SYMBOL
 int evutil_secure_rng_set_urandom_device_file(char *fname);
 
+#ifdef EVENT__HAVE_ARC4RANDOM_ADDRANDOM
 /** Seed the random number generator with extra random bytes.
 
     You should almost never need to call this function; it should be
@@ -858,6 +859,7 @@ int evutil_secure_rng_set_urandom_device_file(char *fname);
  */
 EVENT2_EXPORT_SYMBOL
 void evutil_secure_rng_add_bytes(const char *dat, size_t datlen);
+#endif
 
 #ifdef __cplusplus
 }