fix compilation error

seed.ce

@@ -54,6 +54,7 @@ var compiled = null
 var optimized = null
 var mcode_json = null
 var out_path = null
+var build_dir = null
 
 // Regenerate pipeline module seeds
 for (i = 0; i < length(pipeline_modules); i++) {
@@ -103,7 +104,7 @@ if (fd.is_file(bootstrap_path)) {
 print('\nRegenerated ' + text(generated) + ' seed(s)')
 
 if (clean) {
-  var build_dir = shop.get_build_dir()
+  build_dir = shop.get_build_dir()
   if (fd.is_dir(build_dir)) {
     print('Clearing build cache: ' + build_dir)
     os.system('rm -rf "' + build_dir + '"')