In mingwrt-3.x, the .def files from which the various
libmsvcr*.a are generated incorporated version specific filters, ensuring that the respective import libraries would expose only those symbols which are expected to be exported by their associated DLLs. WSL-4 has discarded these filters, making the effective export lists for all
libmsvcr*.a identical; (the only exception being the addition of the
_get_output_format() stub, to those import libraries which are associated with DLLs which are known to lack that function).
This, surely, cannot be considered to be an appropriate implementation.