package build failures on netbsd-8 using nbtar, pax, bsdtar

[Greg Troxel <gdt%lexort.com@localhost>]

This is about a system with netbsd-8 built with sources updated on
2020-02-14.

I updated pkgsrc, and several sphinx packages are failing to build.
With help from adam@, I have narrowed it down to bad extraction from the
upstream tarball.

The package is /usr/pkgsrc/textproc/py-sphinxcontrib-serializinghtml
which was recently updated to 1.1.4.  The 1.1.3 tarball looks fine with
NetBSD's /bin/tar but the 1.1.4 throws lots of:

tar: File extended headers posix ustar archive. Extracting as plain files. Following files might be in the wrong directory or have wrong attributes.
----------  1 root     wheel         27 Dec 31  1969 ././@PaxHeader
drwxr-xr-x  2 502      staff          0 Dec 31  1969 sphinxcontrib-serializinghtml-1.1.4/sphinxcontrib/serializinghtml/locales/zh_TW
tar: File extended headers posix ustar archive. Extracting as plain files. Following files might be in the wrong directory or have wrong attributes.
----------  1 root     wheel         28 Dec 31  1969 ././@PaxHeader
drwxr-xr-x  2 502      staff          0 Dec 31  1969 sphinxcontrib-serializinghtml-1.1.4/sphinxcontrib/serializinghtml/locales/zh_TW/LC_MESSAGES
tar: File extended headers posix ustar archive. Extracting as plain files. Following files might be in the wrong directory or have wrong attributes.
----------  1 root     wheel        156 Dec 31  1969 ././@PaxHeader
-rw-r--r--  1 502      staff        755 Dec 31  1969 sphinxcontrib-serializinghtml-1.1.4/sphinxcontrib/serializinghtml/locales/zh_TW/LC_MESSAGES/sphinxco
tar: File extended headers posix ustar archive. Extracting as plain files. Following files might be in the wrong directory or have wrong attributes.
----------  1 root     wheel        156 Dec 31  1969 ././@PaxHeader
-rw-r--r--  1 502      staff       1007 Dec 31  1969 sphinxcontrib-serializinghtml-1.1.4/sphinxcontrib/serializinghtml/locales/zh_TW/LC_MESSAGES/sphinxco

and there is indeed a "sphinxco" file when unpacked.

Using gtar to extract results in an OK build.

So I think something is wrong with the tar on netbsd-8, and I'm not sure
what we should be doing.

The files can be grabbed from:

https://pypi.org/project/sphinxcontrib-serializinghtml/#history
https://files.pythonhosted.org/packages/cd/cc/fd7d17cfae18e5a92564bb899bc05e13260d7a633f3cffdaad4e5f3ce46a/sphinxcontrib-serializinghtml-1.1.3.tar.gz
https://files.pythonhosted.org/packages/ac/86/021876a9dd4eac9dae0b1d454d848acbd56d5574d350d0f835043b5ac2cd/sphinxcontrib-serializinghtml-1.1.4.tar.gz


(There are similar problems with a few other sphinxcontrib-foo packages,
and I'm guessing theya are the same thing.)