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

[via cfe-commits]

SihangZhu wrote:

> As @arichardson noted this would break the ABI.
> 
> The best solution is to fix the implementation of `__unw_add_dynamic_eh_frame_section` (and `__unw_remove_dynamic_eh_frame_section`) as described in [#76957 (comment)](https://github.com/llvm/llvm-project/issues/76957#issuecomment-1879977544).

thx for advice.

https://github.com/llvm/llvm-project/pull/77185