Improve system calls

- Wrap clock_getres()
- Wrap sched_setscheduler()
- Make sleep() api conformant
- Polyfill sleep() using select()
- Improve clock_gettime() polyfill
- Make nanosleep() POSIX conformant
- Slightly improve some DNS functions
- Further strengthen pledge() sandboxing
- Improve rounding of timeval / timespec
- Allow layering of pledge() calls on Linux
- Polyfill sched_yield() using select() on XNU
- Delete more system constants we probably don't need

tool/emacs/cosmo-asm-mode.el

@@ -113,6 +113,7 @@
        "asyncsignalsafe"
        "notasyncsignalsafe"
        "isa"
+       "norestart"
        "mayalias"
        "sideffect")
       "\\>"]))