RFR: 8240259: Disable -Wshift-negative-value warnings

[Magnus Ihse Bursie]

Looks good to me.

/Magnus

On 2020-05-22 03:54, Kim Barrett wrote:
> Please review this change which disables warnings for left shift of a
> negative value when compiling HotSpot with gcc or clang.  This warning
> isn't helpful, given that all compilers seem to do the obvious thing,
> and that obvious thing will soon-ish (C++20) be the specified thing.
> See the CR for more details.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8240259
>
> Webrev:
> https://cr.openjdk.java.net/~kbarrett/8240259/open.00/
>
> Testing:
> mach5 tier1.  Also tier1-5 with C++14 enabled.
>
> Note that there are already occurrences of left shift of negative
> values in our code, with no apparent consequences, even when testing
> with C++11/14 enabled.
>