[libunwind] fix dynamic .eh_frame registration (#77185)

Fix this issue
[#76957](https://github.com/llvm/llvm-project/issues/76957)
Libgcc provides __register_frame to register a dynamic .eh_frame
section, while __unw_add_dynamic_eh_frame_section can be used to do the
same in libunwind. However, the address after dynamic .eh_frame are
padding with 0 value, it will be identified as
legal CIE. And __unw_add_dynamic_eh_frame_section will continue to parse
subsequent addresses until illegal memory or other sections are
accessed.
This patch adds length formal parameter for dynamic registration.