Work even if build/ dir doesn't exist

contrib/devtools/gen-linux-binary-release.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# Copyright (c) 2016-2021 The Hush developers
+# Copyright (c) 2016-2022 The Hush developers
 # Released under the GPLv3
 
 set -e
@@ -11,8 +11,13 @@ VERSION=$(./src/hushd --version|grep version|cut -d' ' -f4|cut -d- -f1|sed 's/v/
 FILE="hush-$VERSION-linux-amd64.tar"
 TIME=$(perl -e 'print time')
 
-mv build build.$TIME
+if [ -d "build" ]
+then
+    mv build build.$TIME
+    echo "Moved existing build/ dir to build.$TIME"
+fi
 mkdir build
+echo "Created new build/ dir"
 cp contrib/asmap/asmap.dat build/
 cp sapling*.params build/
 cd src