[llvm] [BOLT][AArch64] Check Last Element Instead of Returning `nullptr` in `lookupStubFromGroup` (PR #114015)

[Paschalis Mpeis via llvm-commits]

paschalis-mpeis wrote:

> Removing -nostdlib may get some errors

Are you sure? I thought testing like `llvm-lit bolt/test/AArch64/long-jmp-one-stub.s` would work as it's included on AArch64's [config](https://github.com/llvm/llvm-project/blob/0cbdad4bd2396b740742d9ae94cba7d7b8a32cb5/bolt/test/AArch64/lit.local.cfg#L4).

https://github.com/llvm/llvm-project/pull/114015