Correctly propagate toolchain setting in SConstruct.

preparser/SConscript

 # Copyright 2011 the V8 project authors. All rights reserved.
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 from os.path import join
-Import('context')
+Import('context tools')
 
 def ConfigureObjectFiles():
-  env = Environment()
+  env = Environment(tools=tools)
   env.Replace(**context.flags['preparser'])
   context.ApplyEnvOverrides(env)
   return env.Object('preparser-process.cc')
 
 preparser_object = ConfigureObjectFiles()
 Return('preparser_object')