[patch v1] add ptmx support to test-container

[DJ Delorie]

"H.J. Lu" <hjl.tools@gmail.com> writes:
> No need for macros.  We can add tst-ptmx.h to define inline functions,
> devmount_ptmx and mount_ptmx.  Then we just do

Four macros, four inline functions, same thing.  I just don't see the
point.  We either have a lot of kernel-specific information on setting
up a container in test-container.c (the only place that uses it), or we
spread that information around where it's harder to find.