Support for overriding the target toolchain when cross compiling

tools/build.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 #
 
 import optparse
 import os
 import re
@@ skipping 102 matching lines @@
       if 'v8' in args:
         print "The v8 target is not supported for android builds."
         return False
   return True
 
 
 def SetTools(arch, toolchainprefix):
   toolsOverride = None
   if arch == 'arm' and toolchainprefix == None:
     toolchainprefix = DEFAULT_ARM_CROSS_COMPILER_PATH + "/bin/arm-linux-gnueabi"
+  # If the 'TARGET_TOOLCHAIN_PREFIX' environment variable is set, we use it
+  # instead. (We use it currently on our buildbots to override the default
+  # toolchain).
+  if 'TARGET_TOOLCHAIN_PREFIX' in os.environ:
+    toolchainprefix = os.environ['TARGET_TOOLCHAIN_PREFIX']
   if toolchainprefix:
     toolsOverride = {
       "CC.target"  :  toolchainprefix + "-gcc",
       "CXX.target" :  toolchainprefix + "-g++",
       "AR.target"  :  toolchainprefix + "-ar",
       "LINK.target":  toolchainprefix + "-g++",
       "NM.target"  :  toolchainprefix + "-nm",
     }
   return toolsOverride
 
@@ skipping 314 matching lines @@
         process.wait()
         if process.returncode != 0:
           print "BUILD FAILED"
           return 1
 
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(Main())