[clang] [clang][driver][darwin] Use DefaultDeploymentTarget when inferring deployment target from SDK (PR #217983)

[Ian Anderson via cfe-commits]

https://github.com/ian-twilightcoder commented:

I don't know how urgently we need this change, but the correct thing would be to get these values from the matching SupportedTarget. The top level versions shouldn't really be used, but that's a bigger change.

https://github.com/llvm/llvm-project/pull/217983