Makefile util/gen-tarball executable after creating the file.

diff --git a/configure b/configure
index 889bdcd..d38fb25 100644
--- a/configure
+++ b/configure
@@ -15536,3 +15536,5 @@
   $ac_cs_success || { (exit 1); exit 1; }
 fi
 
+if test -f util/gen-tarball; then chmod +x util/gen-tarball; fi
+