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

[Reid Kleckner via llvm-commits]

rnk wrote:

If someone is using modern LLVM to target iOS 3-4, is it reasonable to assume that they are also using a more modern linker that supports the necessary static relocations?

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