Endianess code should use memcpy instead of unions. This apparently
is more correct on old, optimizing compilers. Technically, this is
compilers being really stupid but we work with what we got.
That said, this endianess code is more complicated than needed.
As discused over gitter, `WIFSIGNALED` macro must be checked before one
uses the WTERMSIG macro. This change reflects that necessity and adds a
final else clause which will panic if no status code could be
determined.
Useful for old-style unix daemons, start up scripts, and so on.
Easy to add on top of os/execute.
May want to consider allowing the same IO redirection as os/execute
and os/spawn.
May also want to put both fork and exec behind a config switch since I
suppose some systems may not support them, although I don't know of any
concrete examples.
Instead of setting a flag, each interrupt increments an atomic
counter. When the interrupt is finally handled, either by scheduling
code to run on the event loop or executing some out of band code, the
user must now decrement the interrupt counter with
janet_interpreter_interrupt_handled. While this counter is non-zero, the
event loop will not enter the interpreter. This changes the API a bit but
makes it possible and easy to handle signals without race conditions
or scheduler hacks, as the runtime can ensure that high priority code is
run before re-entering possibly blocking interpreter code again.
Also included is a new function janet_schedule_soon, which prepends to
the task queue instead of appending, allowing interrupt handler to skip
ahead of all other scheduled fibers.
Lastly, also update meson default options to include the
interpreter_interrupt code and raise a runtime error if os/sigaction
is used with interpreter interrupt but that build option is not enabled.
