Detected by evil-izing the widely used `MoveOnly` testing type.
I had to patch some tests that were themselves using its comma operator,
but I think that's a worthwhile cost in order to catch more places
in our headers that needed comma-proofing.
The trick here is that even `++ptr, SomeClass()` can find a comma operator
by ADL, if `ptr` is of type `Evil*`. (A comma between two operands
of non-class-or-enum type is always treated as the built-in
comma, without ADL. But if either operand is class-or-enum, then
ADL happens for _both_ operands' types.)
Differential Revision: https://reviews.llvm.org/D109414
Also, improve tests for std::destroy and std::destroy_n so that they
check for array support.
These changes are part of http://wg21.link/p0896 (the One Ranges proposal).
Differential Revision: https://reviews.llvm.org/D106916
Arthur O'Dwyer