Update psABI to match Itanium C++ ABI fixes for passing class objects indirectly

[zygoloid]

The Itanium C++ ABI was recently fixed to properly determine whether to pass objects of class type in registers in C++11 onwards, taking move constructors into account:

itanium-cxx-abi/cxx-abi@05fc233

Section 3.2.3 of the x86 psABI should be updated to take this into account. Or better, it should simply defer to the Itanium C++ ABI to determine how to pass C++ classes rather than trying to duplicate the specification.

Eg, something like:

If a C++ object has either a non-trivial copy constructor or a non-trivial destructor [Footnote] is non-trivial for the purpose of calls, as specified in the Itanium C++ ABI, it is passed by invisible reference (the object is replaced in the parameter list by a pointer that has class INTEGER)

[hjl-tools]

Does this patch look OK?

0001-Refer-non-trivial-C-object-to-C-ABI.patch.txt

[zygoloid]

Yes, thanks, that patch looks good.

I wonder if we should also update footnote 14: "An object with either a non-trivial copy constructor or a non-trivial destructor cannot be passed by value because such objects must have well defined addresses. Similar issues apply when returning an object from a function."

Perhaps something like: "An object whose type is non-trivial for the purpose of calls cannot be passed by value because such objects must have the same address in the caller and the callee. Similar issues apply when returning an object from a function. See C++17 [class.temporary] paragraph 3."

[hjl-tools]

Would you mind send me a patch?

[zygoloid]

Here: #7