Build the IRT with nacl-clang for x86

src/untrusted/irt/frame_info_stubs.c

+/*
+ * Copyright (c) 2015 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* On x86-64 we build the IRT with sandbox base-address hiding. This means that
+ * all of its components must be built with LLVM's assembler. Currently the
+ * unwinder library is built with nacl-gcc and so does not use base address
+ * hiding. The IRT does not use exceptions, so we do not actually need the
+ * unwinder at all. To prevent it from being linked into the IRT, we provide
+ * stub implementations of its functions that are referenced from crtbegin.c.
+ */
+
+void __register_frame_info(void *begin, void *ob) {}
+void __deregister_frame_info(const void *begin) {}