fix, hygiene, never hand out uninitialised differ pids

Signed-off-by: Sebastian Freundt <hroptatyr@fresse.org>
minor, fail find_tst() when line expansions fail

Signed-off-by: Sebastian Freundt <hroptatyr@fresse.org>
hygiene, hide pty guts behind HAVE_PTY_H guard

Signed-off-by: Sebastian Freundt <hroptatyr@fresse.org>
hygiene, invalidate pty descriptors in pfork()

Signed-off-by: Sebastian Freundt <hroptatyr@fresse.org>
chore, disable ignore_06 test

diffing /dev files is too far off of our use cases.
On AIX /dev/null is strictly WRONLY and would hang.

Signed-off-by: Sebastian Freundt <hroptatyr@fresse.org>
Merge branch 'bld/aix'

* bld/aix:
  chore, disable ignore_06 test
  hygiene, invalidate pty descriptors in pfork()
  hygiene, hide pty guts behind HAVE_PTY_H guard
  minor, fail find_tst() when line expansions fail
  fix, hygiene, never hand out uninitialised differ pids