RFR: JDK-8231974: Build fails if no common legal notices are present

[Magnus Ihse Bursie]

LGTM. 

/Magnus

> 8 okt. 2019 kl. 21:24 skrev Erik Joelsson <erik.joelsson at oracle.com>:
> 
> In certain Oracle build configurations, the common legal output directory is never created, because there are no legal files to put in it. This should not make the build fail. This patch makes adding the --legal-notices parameter to jmod optional.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8231974
> 
> Webrev: http://cr.openjdk.java.net/~erikj/8231974/webrev.01/
> 
> /Erik
>