scons: Remember the options set on the command line.

Save them in config.py
diff --git a/SConstruct b/SConstruct
index 104cc38..6b725c4 100644
--- a/SConstruct
+++ b/SConstruct
@@ -40,6 +40,8 @@
 	ENV = os.environ,
 )
 
+opts.Save('config.py', env)
+
 # Backwards compatability with old target configuration variable
 try:
     targets = ARGUMENTS['targets']