Issue a warning if naclsdk_mode=manual is specified with ARM.

SConstruct

 # -*- python -*-
 # Copyright 2008 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 stat
 import subprocess
@@ skipping 283 matching lines @@
       stdout=subprocess.PIPE, stderr=subprocess.PIPE)
   (stdout, stderr) = p.communicate()
   arm_env = eval(stdout)
   for k in arm_env:
     if k.startswith('NACL_') or k.startswith('ARM_'):
       os.environ[k] = arm_env[k]
 
 
 # Source setup bash scripts and glean the settings.
 if (pre_base_env['TARGET_ARCHITECTURE'] == 'arm' and
-    not ARGUMENTS.get('built_elsewhere') and
-    ARGUMENTS.get('naclsdk_mode') != 'manual'):
-  FixupArmEnvironment()
-
+    not ARGUMENTS.get('built_elsewhere')):
+  if ARGUMENTS.get('naclsdk_mode') != 'manual':
+    FixupArmEnvironment()
+  else:
+    print >>sys.stderr, (
+        "You must not specify naclsdk_mode=manual for ARM (any more).")
+    sys.exit(1);
 
 # ----------------------------------------------------------
 # PLUGIN PREREQUISITES
 # ----------------------------------------------------------
 
 PREREQUISITES = pre_base_env.Alias('plugin_prerequisites', [])
 
 
 def GetPluginPrerequsites():
   # the first source is the banner. drop it
@@ skipping 1278 matching lines @@
 # Generate a solution, defer to the end.
 solution_env = base_env.Clone(tools = ['visual_studio_solution'])
 solution = solution_env.Solution(
     'nacl', environment_list,
     exclude_pattern = '.*third_party.*',
     extra_build_targets = {
         'Firefox': 'c:/Program Files/Mozilla FireFox/firefox.exe',
     },
 )
 solution_env.Alias('solution', solution)