Disabling SCM_CREDS usage on DragonFly BSD.

DragonFly BSD supports SCM_CREDS and SCM_RIGHTS, but only the first control
message is passed correctly while the second one isn't processed by the kernel.

This closes #599 issue on GitHub.

auto/sockets

@@ -166,21 +166,22 @@ if [ $nxt_found = no ]; then
 fi
 
 
-nxt_feature="sockopt SO_PASSCRED"
-nxt_feature_name=NXT_HAVE_SOCKOPT_SO_PASSCRED
-nxt_feature_run=
-nxt_feature_incs=
-nxt_feature_libs=
-nxt_feature_test="#define _GNU_SOURCE
+if [ $NXT_SYSTEM != DragonFly ]; then
+    nxt_feature="sockopt SO_PASSCRED"
+    nxt_feature_name=NXT_HAVE_SOCKOPT_SO_PASSCRED
+    nxt_feature_run=
+    nxt_feature_incs=
+    nxt_feature_libs=
+    nxt_feature_test="#define _GNU_SOURCE
                       #include <sys/socket.h>
 
                       int main() {
                           return SO_PASSCRED == 0;
                       }"
-. auto/feature
+    . auto/feature
 
 
-if [ $nxt_found = yes ]; then
+    if [ $nxt_found = yes ]; then
         nxt_feature="struct ucred"
         nxt_feature_name=NXT_HAVE_UCRED
         nxt_feature_run=
@@ -194,21 +195,22 @@ if [ $nxt_found = yes ]; then
                               return sizeof(struct ucred);
                           }"
         . auto/feature
-fi
+    fi
 
 
-nxt_feature="struct cmsgcred"
-nxt_feature_name=NXT_HAVE_MSGHDR_CMSGCRED
-nxt_feature_run=
-nxt_feature_incs=
-nxt_feature_libs=
-nxt_feature_test="#define _GNU_SOURCE
+    nxt_feature="struct cmsgcred"
+    nxt_feature_name=NXT_HAVE_MSGHDR_CMSGCRED
+    nxt_feature_run=
+    nxt_feature_incs=
+    nxt_feature_libs=
+    nxt_feature_test="#define _GNU_SOURCE
                       #include <sys/socket.h>
 
                       int main() {
                           return sizeof(struct cmsgcred);
                       }"
-. auto/feature
+    . auto/feature
+fi
 
 
 nxt_feature="sys/filio.h"

docs/changes.xml

@@ -59,6 +59,12 @@ appeared in 1.26.0.
 </para>
 </change>
 
+<change type="bugfix">
+<para>
+fatal errors on DragonFly BSD; the bug had appeared in 1.26.0.
+</para>
+</change>
+
 </changes>