add pledge(2) to "mutool extract"

Index: source/tools/pdfextract.c
--- source/tools/pdfextract.c.orig
+++ source/tools/pdfextract.c
@@ -27,8 +27,11 @@
 #include "mupdf/fitz.h"
 #include "mupdf/pdf.h"
 
+#include <unistd.h>
+#include <errno.h>
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
 
 static pdf_document *doc = NULL;
 static fz_context *ctx = NULL;
@@ -295,6 +298,12 @@ int pdfextract_main(int argc, char **argv)
 		return usage();
 
 	infile = argv[fz_optind++];
+
+	if (pledge("stdio rpath wpath cpath", NULL) == -1)
+	{
+		fprintf(stderr, "pledge: %s\n", strerror(errno));
+		exit(1);
+	}
 
 	ctx = fz_new_context(NULL, NULL, FZ_STORE_UNLIMITED);
 	if (!ctx)