[libc] Adjust aarch64 startup code to reliably sniff out the start args.

Since this now allows, the init/fini array iteration has been added in
a similar fashion to x86_64 and the corresponding test enabled.

Reviewed By: jeffbailey

Differential Revision: https://reviews.llvm.org/D131133

GitOrigin-RevId: c9e1ecd46da5c31cd7da3207691567906a100231
2 files changed