The original libunwind project defines UNW_AARCH64_* instead of UNW_ARM64_*.
Rename the enum members to match. This allows some applications with simple
unw_init_local usage to migrate to llvm-project libunwind.
Note: the canonical names of UNW_ARM_D{0..31} are now UNW_AARCH64_V{0..31},
to match the original libunwind.
UNW_ARM64_* are kept for now for compatibility. Some may be unneeded and can be
cleaned up in the future.
Wouldn't mind a new line before this block either.