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

[Tomohiro Kashiwada via cfe-commits]

https://github.com/kikairoya commented:

I've added tests related to #40363 and #66909 .
Is it worth submitting these test-only patches first, to assert the current behavior?

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