Added getentropy() support.

Prodded by David Carlier.

auto/unix

@@ -48,6 +48,49 @@ if [ $nxt_found = no ]; then
 fi
 
 
+if [ $nxt_found = no ]; then
+
+    # OpenBSD 5.6 lacks <sys/random.h>.
+
+    nxt_feature="getentropy()"
+    nxt_feature_name=NXT_HAVE_GETENTROPY
+    nxt_feature_test="#include <unistd.h>
+
+                      int main() {
+                          char  buf[4];
+
+                          if (getentropy(buf, 4) == -1) {
+                              return 1;
+                          }
+
+                          return 0;
+                      }"
+    . auto/feature
+fi
+
+
+if [ $nxt_found = no ]; then
+
+    # macOS 10.12.
+
+    nxt_feature="getentropy() in sys/random.h"
+    nxt_feature_name=NXT_HAVE_GETENTROPY_SYS_RANDOM
+    nxt_feature_test="#include <unistd.h>
+                      #include <sys/random.h>
+
+                      int main() {
+                          char  buf[4];
+
+                          if (getentropy(buf, 4) == -1) {
+                              return 1;
+                          }
+
+                          return 0;
+                      }"
+    . auto/feature
+fi
+
+
 nxt_feature="ucontext"
 nxt_feature_name=NXT_HAVE_UCONTEXT
 nxt_feature_run=