Add #includes needed on some platforms in the new files.

Hopefully this makes the *BSD buildfarm animals happy.

src/backend/access/transam/timeline.c

@@ -32,6 +32,7 @@
 
 #include "postgres.h"
 
+#include <sys/stat.h>
 #include <stdio.h>
 #include <unistd.h>
 

src/backend/access/transam/xlog.c

@@ -15,12 +15,10 @@
 #include "postgres.h"
 
 #include <ctype.h>
-#include <signal.h>
 #include <time.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/time.h>
-#include <sys/wait.h>
 #include <unistd.h>
 
 #include "access/clog.h"

src/backend/access/transam/xlogarchive.c

@@ -16,6 +16,7 @@
 
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/wait.h>
 #include <signal.h>
 #include <unistd.h>