[llvm] Remove iOS 5 check for tailcalls on ARM (PR #133354)

[David Green via llvm-commits]

davemgreen wrote:

I got that from https://github.com/llvm/llvm-project/commit/8decdc472f308b13d7fb7fd50c3919db086c0417 and might be wrong about the reason.
```
  /// SupportsTailCall - True if the OS supports tail call. The dynamic linker
  /// must be able to synthesize call stubs for interworking between ARM and
  /// Thumb.
```

https://github.com/llvm/llvm-project/pull/133354