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

[Tomohiro Kashiwada via cfe-commits]

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kikairoya wrote:

There was a check which has been dropped now:

```c++
      if ((TSK == TSK_ExplicitInstantiationDeclaration ||
           TSK == TSK_ExplicitInstantiationDefinition) &&
           Member->hasAttr<ExcludeFromExplicitInstantiationAttr>())
        continue;
```

since any member shouldn't have both the exclude attribute and the dllimport/dllexport attributes.

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