hg: jdk/sandbox: 8240259: Disable -Wshift-negative-value warnings

[chris.hegarty at oracle.com]

Changeset: c6c981b12f69
Author:    kbarrett
Date:      2020-05-28 21:40 -0400
URL:       https://hg.openjdk.java.net/jdk/sandbox/rev/c6c981b12f69

8240259: Disable -Wshift-negative-value warnings
Summary: Disable warning for gcc/clang.
Reviewed-by: ihse, iklam

! make/hotspot/lib/CompileJvm.gmk