[clang] [clang] Fixup last value in DarwinPlatformKind enum (PR #81011)

[Juergen Ributzka via cfe-commits]

ributzka wrote:

Why didn't this trigger: https://github.com/llvm/llvm-project/blob/ab92f6274b7c3a4b4445d47017bc481aa919545f/clang/lib/Driver/ToolChains/Darwin.cpp#L1906 ?

https://github.com/llvm/llvm-project/pull/81011