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

[Hans Wennborg via cfe-commits]

https://github.com/zmodem commented:

Thanks! I think the code looks good, but I think we can simplify the tests. I've focused on the first file, but the comments apply to both.

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