Allow creating a NaClAppThread without creating a new host OS thread

src/trusted/service_runtime/sel_ldr.h

 /*
  * Copyright (c) 2012 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.
  */
 
 /*
  * NaCl Simple/secure ELF loader (NaCl SEL).
  *
  * This loader can only process NaCl object files as produced using
@@ skipping 497 matching lines @@
  *
  * Also mark nap's exit_status and running member variables, announce
  * via condvar that the nexe should be considered no longer running.
  *
  * Returns true (non-zero) if exit status was reported via the reverse
  * channel, and false (0) otherwise.
  */
 int NaClReportExitStatus(struct NaClApp *nap, int exit_status);
 
 /*
+ * Get the top of the initial thread's stack.  Returns a user address.
+ */
+uintptr_t NaClGetInitialStackTop(struct NaClApp *nap);
+
+/*
  * Used to launch the main thread.  NB: calling thread may in the
  * future become the main NaCl app thread, and this function will
  * return only after the NaCl app main thread exits.  In such an
  * alternative design, NaClWaitForMainThreadToExit will become a
  * no-op.
  */
 int NaClCreateMainThread(struct NaClApp     *nap,
                          int                argc,
                          char               **argv,
                          char const *const  *envp) NACL_WUR;
@@ skipping 250 matching lines @@
 #else
 static INLINE void NaClHandleBootstrapArgs(int *argc_p, char ***argv_p) {
   UNREFERENCED_PARAMETER(argc_p);
   UNREFERENCED_PARAMETER(argv_p);
 }
 #endif
 
 EXTERN_C_END
 
 #endif  /* NATIVE_CLIENT_SRC_TRUSTED_SERVICE_RUNTIME_SEL_LDR_H_ */