RFR: JDK-8196985: Disable new warnings from GCC 7.3 in jdk libraries

[Tim Bell]

Erik:

> When building the jdk with GCC 7.3, a bunch of new warnings are
> triggered. These include:
>
> * implicit-fallthrough
> * shift-negative-value
> * misleading-indentation
> * maybe-uninitialized
>
> I won't attempt to fix any of these at this point, but rather just
> disable the warnings. I have created followup issues (or added to
> existing ones where applicable) for each library/executable where
> warnings need to be evaluated.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8196985
>
> Webrev: http://cr.openjdk.java.net/~erikj/8196985/webrev.01/

Looks good.  Thanks for creating the followup bug reports.

/Tim