Don't copy the ENV variable from the users's external environment into...

SConstruct

Index: SConstruct
===================================================================
--- SConstruct	(revision 2739)
+++ SConstruct	(working copy)
@@ -789,7 +789,16 @@
 
   context = BuildContext(options, env_overrides, samples=SplitList(env['sample']))
 
-  library_flags = context.AddRelevantFlags(os.environ, LIBRARY_FLAGS)
+  # Remove variables which can't be imported from the user's external
+  # environment into a construction environment.
+  user_environ = os.environ.copy()
+  for var in ('ENV',):
+    try:
+      del user_environ[var]
+    except KeyError:
+      pass
+
+  library_flags = context.AddRelevantFlags(user_environ, LIBRARY_FLAGS)
   v8_flags = context.AddRelevantFlags(library_flags, V8_EXTRA_FLAGS)
   mksnapshot_flags = context.AddRelevantFlags(library_flags, MKSNAPSHOT_EXTRA_FLAGS)
   dtoa_flags = context.AddRelevantFlags(library_flags, DTOA_EXTRA_FLAGS)