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

test/libc/calls/clock_gettime_test.c

@@ -30,6 +30,10 @@
 #include "libc/testlib/testlib.h"
 #include "libc/time/time.h"
 
+TEST(clock_gettime, fault) {
+  ASSERT_SYS(EFAULT, -1, clock_gettime(0, 0));
+}
+
 TEST(clock_gettime, test) {
   bool isfast;
   struct timespec ts = {0};