Change built_elsewhere flag to work with pexe mode

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 glob
 import os
 import platform
 import shutil
@@ skipping 1959 matching lines @@
   return ('process_output_single' in extra or
           'log_golden' in extra)
 
 # ----------------------------------------------------------
 DeclareBit('tests_use_irt', 'Non-browser tests also load the IRT image', False)
 
 # Translate the given pexe.
 def GetTranslatedNexe(env, pexe):
   pexe_name = pexe.abspath
   nexe_name = pexe_name[:pexe_name.index('.pexe')] + '.nexe'
-
+  # Make sure the pexe doesn't get removed by the fake builders when
+  # built_elsewhere=1
+  env.Precious(pexe)
   node = env.Command(target=nexe_name, source=[pexe_name],
                      action=[Action('${TRANSLATECOM}', '${TRANSLATECOMSTR}')])
-  # Ignore nexe dependency on pexe and assume it's already there. This replaces
-  # ignoring the test dependency on the nexe, which is what built_elsewhere
-  # does when not in pnacl_generate_pexe mode
-  if env.Bit('built_elsewhere'):
-    env.Ignore(nexe_name, pexe_name)
   return node
 
 pre_base_env.AddMethod(GetTranslatedNexe)
 
 def CommandSelLdrTestNacl(env, name, nexe,
                           args = None,
                           log_verbosity=2,
                           sel_ldr_flags=None,
                           loader=None,
                           size='medium',
@@ skipping 307 matching lines @@
         # of sync with the indexes in "command".
         # See http://code.google.com/p/nativeclient/issues/detail?id=1086
         raise AssertionError('Argument to AutoDepsCommand() actually contains '
                              'multiple (or zero) arguments: %r' % arg)
       if posix_path:
         command[index] = '${SOURCES[%d].posix}' % len(deps)
       else:
         command[index] = '${SOURCES[%d].abspath}' % len(deps)
       deps.append(arg)
 
-  # If we are testing build output captured from elsewhere,
-  # ignore build dependencies, (except pexe translation, which we always
-  # want to do in pnacl_generate_pexe mode)
-  if env.Bit('built_elsewhere') and not env.Bit('pnacl_generate_pexe'):
-    env.Ignore(name, deps)
-  else:
-    env.Depends(name, extra_deps)
+  # If built_elsewhere, build commands are replaced by no-ops, so make sure
+  # the targets don't get removed first
+  if env.Bit('built_elsewhere'):
+    env.Precious(deps)
+  env.Depends(name, extra_deps)
 
   if disabled:
     return env.DisabledCommand(name, deps)
   else:
     return env.Command(name, deps, ' '.join(command))
 
 
 pre_base_env.AddMethod(AutoDepsCommand)
 
 # ----------------------------------------------------------
@@ skipping 546 matching lines @@
         CCFLAGS = ['-m32', ],
         LINKFLAGS = ['-m32', '-L/usr/lib32', ],
         )
   elif linux_env.Bit('build_x86_64'):
     linux_env.Prepend(
         CCFLAGS = ['-m64', ],
         LINKFLAGS = ['-m64', '-L/usr/lib64', ],
         )
   elif linux_env.Bit('build_arm'):
     if linux_env.Bit('built_elsewhere'):
-      # force an unusable environment here
-      linux_env.Replace(CC='NO-ARM-CC-INVOCATION-ALLOWED',
-                        CXX='NO-ARM-CXX-INVOCATION-ALLOWED',
-                        LD='NO-ARM-LD-INVOCATION-ALLOWD',
-                        )
+      def FakeInstall(dest, source, env):
+        print 'Not installing', dest
+      # Replace build commands with no-ops
+      linux_env.Replace(CC='true', CXX='true', LD='true',
+                        AR='true', RANLIB='true', INSTALL=FakeInstall)
+      # Allow emulation on x86 hosts for testing built_elsewhere flag
+      if not platform.machine().startswith('arm'):
+        jail = '${SCONSTRUCT_DIR}/toolchain/linux_arm-trusted'
+        linux_env.Replace(EMULATOR=jail + '/run_under_qemu_arm')
+
     ###############################################################
     # EXPERIMENTAL
     # This is needed to switch to a different trusted cross
     # toolchain when compiling within the cros_chroot
     # BUG=http://code.google.com/p/chromium/issues/detail?id=61695
     # BUG=http://code.google.com/p/chromium/issues/detail?id=38909
     # BUG=http://code.google.com/p/nativeclient/issues/detail?id=135
     #
     elif linux_env.Bit('cros_chroot'):
         # TODO(mseaborn): It would be clearer just to inline
@@ skipping 993 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:')