Commit Briefs
fix sndio detection
the compiler may complain that there's no return: tests.c: In function 'main': tests.c:954: warning: control reaches end of non-void function spotted by the OpenBSD bulk builds on sparc64 (using gcc 4.2)
fix landlock detection
apparently it's not always possible to include both linux/prctl.h and sys/prctl.h.
use (a modified version of) kristaps' oconfigure
see GitHub issue #1