Exported declaration of `std::exception` follows non-exported declaration

[AndreyG]

In the header <exception> firstly <vcruntime_exception.h> is included and then class exception is redeclared as exported. This is incorrect by the standard (https://eel.is/c++draft/module.interface#6), namely it repeats https://eel.is/c++draft/module.interface#example-4, where struct S is replaced with class exception.

[StephanTLavavej]

Reported internal compiler bug VSO-1953157 "Modules: MSVC should emit an error when an exported declaration follows a non-exported declaration".

[StephanTLavavej]

Thanks again for reporting this bug - fixing it was surprisingly involved but it's going to significantly improve and simplify our code! 😻