[llvm] [AArch64][PAC] Don't skip global legalization for AUTH_TCRETURN (PR #182513)

[via llvm-commits]

eleviant wrote:

> this way, it may be worth restoring the original [256 x i8] type which is more natural than executing the value stored in ptr as 8 bytes of instructions

I don't get this. The code calls function located at address pointed by @global, which is clearly expressed by test lines:
```
; CHECK:              adrp    x0, global
; CHECK-NEXT:    add x0, x0, :lo12:global
; CHECK-NEXT:    braaz   x0
```
While initial value of pointer is nullptr, dynamic linker is free to relocate it to whatever seems reasonable, not mandatory limited to 8 bytes in size

https://github.com/llvm/llvm-project/pull/182513