[clang] [analyzer] Rename z3 constraint manager backend to unsupported-z3 (PR #205370)

[Balázs Benics via cfe-commits]

steakhal wrote:

This patch was prompted by https://github.com/llvm/llvm-project/issues/205037#issuecomment-4767923354

https://github.com/llvm/llvm-project/pull/205370