P3092 R0 Modules ABI requirement

[wg21bot]

P3092R0 Modules ABI requirement (Chuanqi Xu)

[Bigcheese]

SG15's general principles for modules ABI:

1. For every named module importable unit, there is always exactly one object that is produced from that same source.
2. For the object produced for a named module importable unit, every exported declaration should be considered used.
3. There is a desire for being able to consider used inline entities attached to a named module as available_externally in importing TUs.

SF	F	N	A	SA
4	5	1	0	0

SG15 Agrees

Microsoft's existing ABI already follows these.

Additionally, SG15 would like to meet with the itanium group to help clarify modules semantics.

Related to: itanium-cxx-abi/cxx-abi#170