[llvm] [WindowsDriver] Always consider `WinSdkVersion` (PR #130377)

[Fabrice de Gans via llvm-commits]

Steelskin wrote:

> I'm not sure if we should do this check this way. Similar to the other arguments if the user specifies the value, we should assume that it is correct rather than basing it on a check that the path exists.

Thanks, I changed it so we always just use the user-provided version.

https://github.com/llvm/llvm-project/pull/130377