Upgrade Embree to the latest official release.

Since Embree v3.13.0 supports AARCH64, switch back to the
official repo instead of using Embree-aarch64.

`thirdparty/embree/patches/godot-changes.patch` should now contain
an accurate diff of the changes done to the library.

thirdparty/embree/common/sys/regression.cpp

@@ -0,0 +1,30 @@
+// Copyright 2009-2021 Intel Corporation
+// SPDX-License-Identifier: Apache-2.0
+
+#include "regression.h"
+
+namespace embree
+{
+  /* registerRegressionTest is invoked from static initializers, thus
+   * we cannot have the regression_tests variable as global static
+   * variable due to issues with static variable initialization
+   * order. */
+  std::vector<RegressionTest*>& get_regression_tests()
+  {
+    static std::vector<RegressionTest*> regression_tests;
+    return regression_tests;
+  } 
+
+  void registerRegressionTest(RegressionTest* test) 
+  {
+    get_regression_tests().push_back(test);
+  }
+
+  RegressionTest* getRegressionTest(size_t index)
+  {
+    if (index >= get_regression_tests().size())
+      return nullptr;
+    
+    return get_regression_tests()[index];
+  }
+}