[llvm] [llvm] get cl::opt instantiations working with MSVC DLL build (PR #147810)

[Vassil Vassilev via llvm-commits]

vgvassilev wrote:

> @compnerd @vgvassilev this one is a bit weird. I did some digging, and MSVC definitely has some quirks around exporting template instances. I will do another pass through the other exported template instances to see if there are any similar situations that didn't fail to link.

I wonder in what other occurrences of similar patterns things got exported mining the field for similar (but not yet seen) issues?

https://github.com/llvm/llvm-project/pull/147810