RFR: 8239357: Revert gcc implementation of offset_of

[Kim Barrett]

> On Apr 22, 2020, at 9:28 AM, Erik Joelsson <erik.joelsson at oracle.com> wrote:
> 
> Build change looks good.

Thanks.

> 
> /Erik
> 
> On 2020-04-22 06:23, Kim Barrett wrote:
>> Please review this change to undo the (small) portion of JDK-8238281
>> [1] related to the HotSpot offset_of macro for gcc/clang.  That change
>> should not have been made.  See CR for details.
>> 
>> I did not reinstate the redefinition of offsetof; we shouldn't be
>> using that macro, and having the warning enabled will catch
>> questionable cases.  (I also considered but didn’t poison it.)
>> 
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8239357
>> 
>> [1] https://bugs.openjdk.java.net/browse/JDK-8238281
>> 
>> Webrev:
>> https://cr.openjdk.java.net/~kbarrett/8239357/open.00/
>> 
>> Testing:
>> mach5 tier1
>> 
>> With a temporary change to use offsetof with a non-standard-layout class,
>> verified the expected build failures occur with gcc and clang.