Revert of Build the IRT with nacl-clang for x86

SConstruct

 #! -*- python -*-
 # 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.
 
 import atexit
 import json
 import os
 import platform
 import re
@@ skipping 3460 matching lines @@
 
 
 # The IRT-building environment was cloned from nacl_env, but it should
 # ignore the --nacl_glibc, nacl_pic=1 and bitcode=1 switches.
 # We have to reinstantiate the naclsdk.py magic after clearing those flags,
 # so it regenerates the tool paths right.
 # TODO(mcgrathr,bradnelson): could get cleaner if naclsdk.py got folded back in.
 nacl_irt_env.ClearBits('nacl_glibc')
 nacl_irt_env.ClearBits('nacl_pic')
 nacl_irt_env.ClearBits('nacl_clang')
-nacl_irt_env.ClearBits('pnacl_generate_pexe')
-nacl_irt_env.ClearBits('use_sandboxed_translator')
-
 # The choice of toolchain used to build the IRT does not depend on the toolchain
-# used to build user/test code. PNaCl is used on mips because that's currently
-# the only compiler for mips. nacl-clang is used on x86.
-if nacl_irt_env.Bit('build_mips32'):
+# used to build user/test code. The PNaCl toolchain is used on x86, except on
+# Windows (because pnacl-clang doesn't run on Windows XP. If we stop supporting
+# building on XP, we can remove this exception).  See
+# https://code.google.com/p/nativeclient/issues/detail?id=3936
+if (nacl_irt_env.Bit('build_mips32') or nacl_irt_env.Bit('build_x86_64') or
+    (nacl_irt_env.Bit('build_x86_32') and
+     not nacl_irt_env.Bit('host_windows'))):
   nacl_irt_env.SetBits('bitcode')
 else:
   nacl_irt_env.ClearBits('bitcode')
-if nacl_irt_env.Bit('build_x86_64') or nacl_irt_env.Bit('build_x86_32'):
-  nacl_irt_env.SetBits('nacl_clang')
-  # The IRT must be built using LLVM's assembler on x86-64 to preserve sandbox
-  # base address hiding (a security hardening mechanism).
-  # It's also used on x86-32 for consistency.
-  # See https://code.google.com/p/nativeclient/issues/detail?id=1235
-  nacl_irt_env.Append(CCFLAGS=['-integrated-as'])
-  if nacl_irt_env.Bit('build_x86_32'):
-    # The x86-32 IRT needs to be callable with an under-aligned stack.
-    # See https://code.google.com/p/nativeclient/issues/detail?id=3935
-    nacl_irt_env.Append(CCFLAGS=['-mstackrealign', '-mno-sse'])
-
+nacl_irt_env.ClearBits('pnacl_generate_pexe')
+nacl_irt_env.ClearBits('use_sandboxed_translator')
 nacl_irt_env.Tool('naclsdk')
 # These are unfortunately clobbered by running Tool, which
 # we needed to do to get the destination directory reset.
 # We want all the same values from nacl_env.
 nacl_irt_env.Replace(EXTRA_CFLAGS=nacl_env['EXTRA_CFLAGS'],
                      EXTRA_CXXFLAGS=nacl_env['EXTRA_CXXFLAGS'],
                      CCFLAGS=nacl_env['CCFLAGS'],
                      CFLAGS=nacl_env['CFLAGS'],
                      CXXFLAGS=nacl_env['CXXFLAGS'])
 FixWindowsAssembler(nacl_irt_env)
 # Make it find the libraries it builds, rather than the SDK ones.
 nacl_irt_env.Replace(LIBPATH='${LIB_DIR}')
 
 if nacl_irt_env.Bit('bitcode'):
-  nacl_irt_env.Append(LINKFLAGS=['--pnacl-allow-native'])
-  if nacl_irt_env.Bit('build_mips32'):
+  if nacl_irt_env.Bit('build_x86_64'):
+    nacl_irt_env.Append(CCFLAGS=['--target=x86_64-unknown-nacl'])
+    nacl_irt_env.Append(LINKFLAGS=['--target=x86_64-unknown-nacl',
+                                   '--pnacl-allow-translate',
+                                   '-arch', 'x86-64'])
+  elif nacl_irt_env.Bit('build_x86_32'):
+    nacl_irt_env.Append(CCFLAGS=['--target=i686-unknown-nacl'])
+    # X86-32 IRT needs to be callable with an under-aligned stack, so we disable
+    # SSE instructions, which can fault on misaligned addresses: see
+    # https://code.google.com/p/nativeclient/issues/detail?id=3935
+    nacl_irt_env.Append(LINKFLAGS=['--target=i686-unknown-nacl',
+                                   '--pnacl-allow-translate',
+                                   '-arch', 'x86-32',
+                                   '-Wt,-mattr=-sse'])
+  elif nacl_irt_env.Bit('build_mips32'):
     # Disable the PNaCl IRT verifier since it will complain about
     # __executable_start symbol not being a valid external symbol.
     nacl_irt_env.Append(LINKFLAGS=['--pnacl-disable-abi-check'])
 
 # The IRT is C only, don't link with the C++ linker so that it doesn't
 # start depending on the C++ standard library and (in the case of
 # libc++) pthread.
 nacl_irt_env.Replace(LINK=(nacl_irt_env['LINK'].
                            replace('pnacl-clang++', 'pnacl-clang')))
-nacl_irt_env.Replace(LINK=(nacl_irt_env['LINK'].
-                           replace('nacl-clang++', 'nacl-clang')))
 
+if nacl_irt_env.Bit('bitcode'):
+  nacl_irt_env.Append(LINKFLAGS=['--pnacl-allow-native'])
 
 # All IRT code must avoid direct use of the TLS ABI register, which
 # is reserved for user TLS.  Instead, ensure all TLS accesses use a
 # call to __nacl_read_tp, which the IRT code overrides to segregate
 # IRT-private TLS from user TLS. This only applies to mips now, on
 # other platforms we modify the TLS register through tls_edit as a
 # post process.
 if nacl_irt_env.Bit('build_mips32'):
   nacl_irt_env.Append(LINKFLAGS=['-Wt,-mtls-use-call'])
 
@@ skipping 474 matching lines @@
   nacl_env.ValidateSdk()
 
 if BROKEN_TEST_COUNT > 0:
   msg = "There are %d broken tests." % BROKEN_TEST_COUNT
   if GetOption('brief_comstr'):
     msg += " Add --verbose to the command line for more information."
   print msg
 
 # separate warnings from actual build output
 Banner('B U I L D - O U T P U T:')