pkg_tar nonfunctional with py_library

[tsr-boxbot]

I have a py_library setup and when I used pkg_tar I get an empty tar as output:

py_library(
    name = 'x_pylib',
    data = [
        ':x_py.so'
    ],
    imports=['.'],
    visibility = ["//visibility:public"],
)

pkg_tar(                                                                                                                                                     
    name = "x-pkg",                                                                                                                                   
    srcs = [                                                                                                                                                 
        "//x-pylib"                                                                                                               
    ],
    package_file_name = "x-amd64-debug.tar",
)

[aiuto]

This looks like another instance of runfiles not being supported correctly. So this is a duplicate of other bugs, but it's too late at night for me to bother looking up which one. I'll do that when I next do triage.

[aiuto]

Dup of #153