On darwin, install_name_tool can be used to relocate binaries/libraries. This
adds support for adjusting them with relative paths rather than hardcoded ones.
The Linux code is factored out into a function but is otherwise unchanged.
(From OE-Core rev: ed5ace3437eb0f751172e6b93399639c94b89e59)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>