Add missing header declarations for pg_basebackup and pg_{dump,restore}

This fixes two compilation failures caused by 6f164e6.  Interesting to
see that missing <limits.h> dies not fail in Linux or even Windows.  On
MacOS, it fails, though.

Per various buildfarm members.

src/bin/pg_basebackup/pg_basebackup.c

@@ -15,6 +15,7 @@
 
 #include <unistd.h>
 #include <dirent.h>
+#include <limits.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
 #include <signal.h>

src/bin/pg_dump/parallel.h

@@ -16,6 +16,8 @@
 #ifndef PG_DUMP_PARALLEL_H
 #define PG_DUMP_PARALLEL_H
 
+#include <limits.h>
+
 #include "pg_backup_archiver.h"
 
 /* Function to call in leader process on completion of a worker task */