[llvm] [llvm] DLLExport public methods from SmallVector (PR #127850)

[Saleem Abdulrasool via llvm-commits]

compnerd wrote:

@kuhar that RFC/discussion has happened multiple times over now. The last time I brought this up was at https://discourse.llvm.org/t/supporting-llvm-build-llvm-dylib-on-windows. There was a follow up GSoC project https://discourse.llvm.org/t/support-clang-plugins-on-windows. There are plenty of related discussion on the forums.

This work enables building LLVM as a DLL on Windows and to enable building plugins for clang on Windows.

https://github.com/llvm/llvm-project/pull/127850