_Page
NULL: defining as const too strict
_sys_mmap
sighandler_t
Explicit include which test got implicitly
_sys_munmap
getpid()

Forego _sys_getpid(), as it cannot fail (at least on Linux)
_sys_exit -> _exit. Forego _sys_... wrappers for calls which cannot fail
_exit: clobbers do not matter, of course
_SystemCallResult_as_FileDescriptor -> ..._as_fd, as we cannot always express these as identifiers, anyway
_WaitFlags -> _WaitOptions, "options" being the documented argument
Define the `int` typedefs in terms of the platform `_Int`
sigval_t
clock_t test
pid_t test
_sys_fork
_WaitidType -> _WaitType, to avoid case confusion
The mess that is `siginfo_t`
struct rusage, needed for _sys_waitid
CLD_...