hg: jdk/submit: 8237479: 8230305 causes slowdebug build failure

[sgehwolf at redhat.com]

Changeset: 4548566f5351
Author:    sgehwolf
Date:      2020-01-18 20:54 +0100
URL:       https://hg.openjdk.java.net/jdk/submit/rev/4548566f5351

8237479: 8230305 causes slowdebug build failure
Summary: Declare methods as pure virtual.
Reviewed-by: duke

! src/hotspot/os/linux/cgroupSubsystem_linux.hpp