This PR allows the entire depends/<host_prefix>
directory to be relocatable.
Only libevent
package configuration files are non-relocatable for the version 2.1.12-stable
we use now. However, this issue has been fixed upstream in https://github.com/libevent/libevent/commit/1f1593ff27bdf51c3e1c45b92cfb0ac931960298 and friends.