[clang] [llvm] [AArch64][PAC] Sign block addresses used in indirectbr. (PR #97647)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Under the proposed ABI, `&&A-&&B` is actually "sign(A)-sign(B)".  Which is a constant, but not one which can be represented as a relocation (as far as I know).

https://github.com/llvm/llvm-project/pull/97647