US082 10.03 [module.import] Define order of initialization for globals in modules P1874

[wg21bot]

The order of initialization of globals in interface and header units is not defined for imported modules. This has the potential to break code, including iostream, when moving to modules.

Proposed change:
Define an ordering. See P1874r0 for details.

[jfbastien]

See cplusplus/papers#624

[davidstone]

SG2 recommends accepting US082 with modifications by accepting P1874. P1874 suggests two models for global initialization dependency structure, named in the paper as "relaxed clang model" and "dependency order model". SG2 has consensus for accepting either of those models, but has stronger consensus for the "relaxed clang model".

[jensmaurer]

CWG in Belfast: Accepted.