[PAC][ELF] Implement codegen support for signed constants

[asl]

After #83788 the downstream implementation that uses wrapper globals should be rewritten to use special ptrauth constant type

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

Author: Anton Korobeynikov (asl)

After https://github.com//issues/83788 the downstream implementation that uses wrapper globals should be rewritten to use special `ptrauth` constant type