List implicit operator== after implicit destructors in a vtable.

Summary:
We previously listed first declared members, then implicit operator=,
then implicit operator==, then implicit destructors. Per discussion on
https://github.com/itanium-cxx-abi/cxx-abi/issues/88, put the implicit
equality comparison operators at the very end, after all special member
functions.

This reinstates add2b7e4, reverted in
commit 89e43f04, with a fix for 32-bit
targets.

Reviewers: rjmccall

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D72897