fix(migration): declare write_cache_format_file before ensure_runtime_cache_format (no hoisting in ucode)

tachyon/files/usr/lib/config/migration.uc

@@ -1486,6 +1486,13 @@ function ensure_runtime_dirs() {
     ensure_dir(TACHYON_SECTION_CACHE_DIR);
 }
 
+function write_cache_format_file(path, format) {
+    let tmp = path + ".tmp";
+    if (fs.writefile(tmp, format + "\n") == null)
+        return null;
+    return fs.rename(tmp, path) ? path : null;
+}
+
 function ensure_runtime_cache_format() {
     ensure_dir(TACHYON_RUNTIME_STATE_DIR);
 
@@ -1508,13 +1515,6 @@ function ensure_runtime_cache_format() {
     }
 }
 
-function write_cache_format_file(path, format) {
-    let tmp = path + ".tmp";
-    if (fs.writefile(tmp, format + "\n") == null)
-        return null;
-    return fs.rename(tmp, path) ? path : null;
-}
-
 function remove_legacy_server_country_cache() {
     // Absent file already satisfies the caller; fs.unlink throws on ENOENT.
     try { fs.unlink(TACHYON_RUNTIME_STATE_DIR + "/server-country-cache.json"); } catch(e) {}