Also, if you set a relative path in native-comp-eln-load-path (directly, not via `startup-redirect-eln-cache'), it defaults to `invocation-directory', which is (in an in-place run) the src/ subdir. 

Which is weird:

(push "./test-native" native-comp-eln-load-path)

and then the test-native/ subdir is created both under `user-emacs-directory' and `invocation-directory' (the .eln files go to the second one).