[clang] [Cygwin] Export global symbols, template instantiations, RTTI and VTable are exported correctly (PR #138773)

[Tomohiro Kashiwada via cfe-commits]

kikairoya wrote:

Thank you. I have divided into separated PRs. They don't have conflict each.

https://github.com/llvm/llvm-project/pull/139797
https://github.com/llvm/llvm-project/pull/139798
https://github.com/llvm/llvm-project/pull/139799



https://github.com/llvm/llvm-project/pull/138773