Neutralize the VirtualThread-unblocker thread

This is not needed as long as espresso doesn't support
continuation-based virtual threads.

Author: gilles-duboscq

espresso/src/com.oracle.truffle.espresso/src/com/oracle/truffle/espresso/substitutions/standard/Target_java_lang_VirtualThread.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2025, 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.oracle.truffle.espresso.substitutions.standard;
+
+import com.oracle.truffle.espresso.substitutions.EspressoSubstitutions;
+import com.oracle.truffle.espresso.substitutions.Substitution;
+
+@EspressoSubstitutions
+public final class Target_java_lang_VirtualThread {
+    private Target_java_lang_VirtualThread() {
+    }
+
+    @Substitution
+    public static void unblockVirtualThreads() {
+        // no-op: loom continuations are not supported
+    }
+}