portability: fix build on Solaris-derived systemd

Current Illumos and older Solaris require _XOPEN_SOURCE for
msg_control. O_DIRECTORY doesn't exist on older systems either,
so fallback to O_RDONLY. It's good enough as a repository will
require both R and X permission anyway.

contrib/chg/hgclient.c

@@ -7,6 +7,11 b''
  * GNU General Public License version 2 or any later version.
  */
 
+#if defined(__sun) && !defined(_XOPEN_SOURCE)
+/* msg_control is used */
+#define _XOPEN_SOURCE 600
+#endif
+
 #include <arpa/inet.h> /* for ntohl(), htonl() */
 #include <assert.h>
 #include <ctype.h>
@@ -26,6 +31,10 b''
 #include "procutil.h"
 #include "util.h"
 
+#ifndef O_DIRECTORY
+#define O_DIRECTORY O_RDONLY
+#endif
+
 enum {
 	CAP_GETENCODING = 0x0001,
 	CAP_RUNCOMMAND = 0x0002,