RFR: JDK-8187681: Compiling for target 9 while also using --patch-module

[Jan Lahoda]

Hello,

I'd like to ask for a review for:
Bug: https://bugs.openjdk.java.net/browse/JDK-8187681
Webrev: http://cr.openjdk.java.net/~jlahoda/8187681/webrev.00/

The patch is basically to remove the limitation on use of --patch-module 
for a system module in combination with --release.

Thanks,
     Jan