hg: jdk/jdk: 8239357: Revert gcc implementation of offset_of

[kim.barrett at oracle.com]

Changeset: d480dcfab743
Author:    kbarrett
Date:      2020-04-23 12:57 -0400
URL:       https://hg.openjdk.java.net/jdk/jdk/rev/d480dcfab743

8239357: Revert gcc implementation of offset_of
Summary: Revert definition of offset_of and reenable -Winvalid-offsetof.
Reviewed-by: erikj, ihse, dholmes

! make/hotspot/lib/CompileJvm.gmk
! src/hotspot/share/utilities/globalDefinitions_gcc.hpp