Fix configure probe for sys/ucred.h.

The configure script's test for <sys/ucred.h> did not work on OpenBSD,
because on that platform <sys/param.h> has to be included first.
As a result, socket peer authentication was disabled on that platform.
Problem introduced in commit be4585b1c27ac5dbdd0d61740d18f7ad9a00e268.

Andres Freund, slightly simplified by me.

configure

@@ -10351,8 +10351,7 @@ done
 
 
 
-
+for ac_header in crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h
-for ac_header in crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/ucred.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h
 do
 as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
 if { as_var=$as_ac_Header; eval "test \"\${$as_var+set}\" = set"; }; then
@@ -10503,7 +10502,7 @@ fi
 done
 
 
-# On BSD, cpp test for net/if.h will fail unless sys/socket.h
+# On BSD, test for net/if.h will fail unless sys/socket.h
 # is included first.
 
 for ac_header in net/if.h
@@ -10572,7 +10571,74 @@ fi
 done
 
 
-# At least on IRIX, cpp test for netinet/tcp.h will fail unless
+# On OpenBSD, test for sys/ucred.h will fail unless sys/param.h
+# is included first.
+
+for ac_header in sys/ucred.h
+do
+as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
+{ $as_echo "$as_me:$LINENO: checking for $ac_header" >&5
+$as_echo_n "checking for $ac_header... " >&6; }
+if { as_var=$as_ac_Header; eval "test \"\${$as_var+set}\" = set"; }; then
+  $as_echo_n "(cached) " >&6
+else
+  cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+$ac_includes_default
+#include <sys/param.h>
+
+
+#include <$ac_header>
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  eval "$as_ac_Header=yes"
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	eval "$as_ac_Header=no"
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+ac_res=`eval 'as_val=${'$as_ac_Header'}
+		 $as_echo "$as_val"'`
+	       { $as_echo "$as_me:$LINENO: result: $ac_res" >&5
+$as_echo "$ac_res" >&6; }
+as_val=`eval 'as_val=${'$as_ac_Header'}
+		 $as_echo "$as_val"'`
+   if test "x$as_val" = x""yes; then
+  cat >>confdefs.h <<_ACEOF
+#define `$as_echo "HAVE_$ac_header" | $as_tr_cpp` 1
+_ACEOF
+
+fi
+
+done
+
+
+# At least on IRIX, test for netinet/tcp.h will fail unless
 # netinet/in.h is included first.
 
 for ac_header in netinet/in.h
@@ -17815,6 +17881,7 @@ cat confdefs.h >>conftest.$ac_ext
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 #include <sys/socket.h>
+#include <sys/param.h>
 #ifdef HAVE_SYS_UCRED_H
 #include <sys/ucred.h>
 #endif
@@ -17853,6 +17920,7 @@ cat confdefs.h >>conftest.$ac_ext
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 #include <sys/socket.h>
+#include <sys/param.h>
 #ifdef HAVE_SYS_UCRED_H
 #include <sys/ucred.h>
 #endif

configure.in

@@ -982,9 +982,9 @@ AC_SUBST(OSSP_UUID_LIBS)
 ##
 
 dnl sys/socket.h is required by AC_FUNC_ACCEPT_ARGTYPES
-AC_CHECK_HEADERS([crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/ucred.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h])
+AC_CHECK_HEADERS([crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h])
 
-# On BSD, cpp test for net/if.h will fail unless sys/socket.h
+# On BSD, test for net/if.h will fail unless sys/socket.h
 # is included first.
 AC_CHECK_HEADERS(net/if.h, [], [],
 [AC_INCLUDES_DEFAULT
@@ -993,7 +993,14 @@ AC_CHECK_HEADERS(net/if.h, [], [],
 #endif
 ])
 
-# At least on IRIX, cpp test for netinet/tcp.h will fail unless
+# On OpenBSD, test for sys/ucred.h will fail unless sys/param.h
+# is included first.
+AC_CHECK_HEADERS(sys/ucred.h, [], [],
+[AC_INCLUDES_DEFAULT
+#include <sys/param.h>
+])
+
+# At least on IRIX, test for netinet/tcp.h will fail unless
 # netinet/in.h is included first.
 AC_CHECK_HEADERS(netinet/in.h)
 AC_CHECK_HEADERS(netinet/tcp.h, [], [],
@@ -1133,6 +1140,7 @@ PGAC_TYPE_LOCALE_T
 
 AC_CHECK_TYPES([struct cmsgcred], [], [],
 [#include <sys/socket.h>
+#include <sys/param.h>
 #ifdef HAVE_SYS_UCRED_H
 #include <sys/ucred.h>
 #endif])