Revert of Reland: Introduce sys_sigprocmask and sys_sigaction.

sandbox/linux/system_headers/arm_linux_ucontext.h

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef SANDBOX_LINUX_SYSTEM_HEADERS_ARM_LINUX_UCONTEXT_H_
-#define SANDBOX_LINUX_SYSTEM_HEADERS_ARM_LINUX_UCONTEXT_H_
-
-#if !defined(__BIONIC_HAVE_UCONTEXT_T)
-#if !defined(__native_client_nonsfi__)
-#include <asm/sigcontext.h>
-#else
-// In PNaCl toolchain, sigcontext and stack_t is not defined. So here declare
-// them.
-struct sigcontext {
-  unsigned long trap_no;
-  unsigned long error_code;
-  unsigned long oldmask;
-  unsigned long arm_r0;
-  unsigned long arm_r1;
-  unsigned long arm_r2;
-  unsigned long arm_r3;
-  unsigned long arm_r4;
-  unsigned long arm_r5;
-  unsigned long arm_r6;
-  unsigned long arm_r7;
-  unsigned long arm_r8;
-  unsigned long arm_r9;
-  unsigned long arm_r10;
-  unsigned long arm_fp;
-  unsigned long arm_ip;
-  unsigned long arm_sp;
-  unsigned long arm_lr;
-  unsigned long arm_pc;
-  unsigned long arm_cpsr;
-  unsigned long fault_address;
-};
-
-typedef struct sigaltstack {
-  void* ss_sp;
-  int ss_flags;
-  size_t ss_size;
-} stack_t;
-
-#endif
-
-// We also need greg_t for the sandbox, include it in this header as well.
-typedef unsigned long greg_t;
-
-// typedef unsigned long sigset_t;
-typedef struct ucontext {
-  unsigned long uc_flags;
-  struct ucontext* uc_link;
-  stack_t uc_stack;
-  struct sigcontext uc_mcontext;
-  sigset_t uc_sigmask;
-  /* Allow for uc_sigmask growth.  Glibc uses a 1024-bit sigset_t.  */
-  int __not_used[32 - (sizeof(sigset_t) / sizeof(int))];
-  /* Last for extensibility.  Eight byte aligned because some
-     coprocessors require eight byte alignment.  */
-  unsigned long uc_regspace[128] __attribute__((__aligned__(8)));
-} ucontext_t;
-
-#else
-#include <sys/ucontext.h>
-#endif  // __BIONIC_HAVE_UCONTEXT_T
-
-#endif  // SANDBOX_LINUX_SYSTEM_HEADERS_ARM_LINUX_UCONTEXT_H_