include: linker: Add missing symbols needed for LLVM's libunwind

LLVM's libunwind needs eh_frame_start/eh_frame_end and
eh_frame_hdr_start/eh_frame_hdr_end symbols.

See
https://github.com/llvm/llvm-project/blob/80267f81482486977b3bdecf3855fc6a3096f912/libunwind/src/AddressSpace.hpp#L73-L103



Signed-off-by: Tom Hughes <tomhughes@chromium.org>