df4d56307b
rustc_codegen_ssa: Don't drop `IncorrectCguReuseType` , make `rustc_expected_cgu_reuse` attr work
In [100753], `IncorrectCguReuseType` accidentally stopped being emitted by removing `diag.span_err(...)`. Begin emitting it again rather than just blindly dropping it, and adjust tests accordingly.
We assume that there are no bugs and that the currently actual CGU reuse is correct. If there are bugs, they will be discovered and fixed eventually, and the tests will then be updated.
[100753]: 706452eba7 (diff-048389738ddcbe0f9765291a29db1fed9a5f03693d4781cfb5aaa97ffb3c7f84)
Closes #118972
Please read the rustc-dev-guide chapter on Backend Agnostic Codegen.