[clang] [Clang] Apply exclude_from_explicit_instantiation to dllimport/dllexport (PR #168171)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

Thanks!

If I remember correctly, there are a number of preexisting references to the problem that `exclude_from_explicit_instantiation` doesn't do what it would need to do on Windows; I think such references may exist in libcxx and/or as other issues here on github. It would be a nice extra if we could find some of those references, to get more stakeholders aware of this change here (and possibly know which references to update).

I'm not very familiar with the code here so I'm not sure if I can do an authoritative review - but it practically looks reasonable. Looping in @zmodem who either can do a more confident review, or find more reviewers.

https://github.com/llvm/llvm-project/pull/168171