RFR: JDK-8215635: Pandoc check in Docs.gmk does not work on Windows

[Magnus Ihse Bursie]

Lgtm. 

/Magnus

> 19 dec. 2018 kl. 12:40 skrev Erik Joelsson <erik.joelsson at oracle.com>:
> 
> Hello,
> 
> In JDK-8214910 a check for if the PANDOC variable had a value was added to Docs.gmk. This check does not work correctly on Windows where PANDOC will always have the fixpath prefix. This patch adds a separate ENABLE_PANDOC variable that make can check.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8215635
> 
> Webrev: http://cr.openjdk.java.net/~erikj/8215635/webrev.01/
> 
> /Erik
>