ARM64: remove stack pushes without frame in RegExpExecStub.

test/mjsunit/regress/regress-487981.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags:  --allow-natives-syntax --stress-compaction
+
+// To reliably reproduce the crash use --verify-heap --random-seed=-133185440
+
+function __f_2(o) {
+  return o.field.b.x;
+}
+
+try {
+  %OptimizeFunctionOnNextCall(__f_2);
+  __v_1 = __f_2();
+} catch(e) { }
+
+function __f_3() { __f_3(/./.test()); };
+
+try {
+__f_3();
+} catch(e) { }