libarchive fails tests on i686

[Ricardo Wurmus]

Hi Guix,

libarchive fails two tests in tar/test/test_option_b.  Here is the test
output:

  test_option_b

  tar/test/test_option_b.c:41: File archive1.tar has size 3072, expected 2048
     Description: bsdtar does not pad archives written directly to regular files
  tar/test/test_option_b.c:63: File archive5.tar has size 3072, expected 2048

libarchive has not yet been built for i686 on hydra, so there are no
binary substitutes available.  The failure to build libarchive blocks
other packages such as qt.

Should we disable the tests for now or does anyone know how to fix them?

~~ Ricardo