It turns out that a lot of 3rd party software does things like:
#ifdef EINTR
...
#endif
This won't work if EINTR is an enum. So much for that nice idea.
The idea here is to combine a potential syscall error code with an arbitrary
type in the case of success. I feel like this will end up much less error
prone than returning some arbitrary type that kinda sorta has bool semantics
(but sometimes not really) and passing the error through an out-param.
This patch only converts a few syscalls to using it. More to come.
