The mkShell should set NIX_NO_SELF_RPATH = true; by default #173025
Description
The mkShell is intended to create a shell to be used by nix-shell. Therefore it's $out doesn't even exist.
Recently there was a PR #153194 that made the shell buildable, but I still think this should be the default.
The NIX_NO_SELF_RPATH = true; would ensure that $out/lib64 and $out/lib does not appear in the $NIX_LDFLAGS, and this would ensure that any compiled objects in that shell do not get these non-existent paths in their rpath.