mariabackup little FreeBSD update support.

In this platform, it s better not to rely on optional proc filesystem presence.
 Using native API to retrieve binary absolute path instead.

extra/mariabackup/xtrabackup.cc

@@ -58,13 +58,17 @@ Street, Fifth Floor, Boston, MA 02110-1335 USA
 
 #ifdef __linux__
 # include <sys/prctl.h>
-#include <sys/resource.h>
+# include <sys/resource.h>
 #endif
 
 #ifdef __APPLE__
 # include "libproc.h"
 #endif
 
+#ifdef __FreeBSD__
+# include <sys/sysctl.h>
+#endif
+
 
 #include <btr0sea.h>
 #include <dict0priv.h>
@@ -6718,6 +6722,11 @@ static int get_exepath(char *buf, size_t size, const char *argv0)
     buf[ret] = 0;
     return 0;
   }
+#elif defined(__FreeBSD__)
+  int mib[4] = {CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1};
+  if (sysctl(mib, 4, buf, &size, NULL, 0) == 0) {
+    return 0;
+  }
 #endif
 
   return my_realpath(buf, argv0, 0);