pextlib1.0: Sort includes, add stdio.h for getline(3) on Linux

Linux requires stdio.h for getline(3), and fails without it. We ship
a getline.h compat implementation, but that doesn't get included unless
HAVE_GETLINE isn't defined, which isn't the case on Linux.

src/pextlib1.0/system.c

@@ -46,18 +46,19 @@
 #include <paths.h>
 #endif
 
-#include <sys/types.h>
-#include <sys/wait.h>
-#include <sys/resource.h>
 #include <assert.h>
+#include <errno.h>
 #include <fcntl.h>
+#include <limits.h>
+#include <signal.h>
 #include <stdbool.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/resource.h>
+#include <sys/types.h>
+#include <sys/wait.h>
 #include <unistd.h>
-#include <limits.h>
-#include <errno.h>
-#include <signal.h>
 
 #include "system.h"
 #include "Pextlib.h"