How to disable demos

[Ioi Lam]

I tried the NO_DEMOS flag as in 
https://bugs.openjdk.java.net/browse/JDK-7143162 "Allow disabling of jdk 
demos and samples build", but this seems to be in "old build" only, and 
doesn't affect the new build system.

Is there an equivalent for the new build?
Thanks

- Ioi