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

libc/sysv/consts/scm.h

@@ -0,0 +1,23 @@
+#ifndef COSMOPOLITAN_LIBC_SYSV_CONSTS_SCM_H_
+#define COSMOPOLITAN_LIBC_SYSV_CONSTS_SCM_H_
+#include "libc/runtime/symbolic.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+extern const long SCM_TIMESTAMP;
+extern const long SCM_CREDENTIALS;
+extern const long SCM_TIMESTAMPING;
+extern const long SCM_TIMESTAMPNS;
+extern const long SCM_WIFI_STATUS;
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+
+#define SCM_RIGHTS       LITERALLY(1)
+#define SCM_TIMESTAMP    SYMBOLIC(SCM_TIMESTAMP)
+#define SCM_CREDENTIALS  SYMBOLIC(SCM_CREDENTIALS)
+#define SCM_TIMESTAMPING SYMBOLIC(SCM_TIMESTAMPING)
+#define SCM_TIMESTAMPNS  SYMBOLIC(SCM_TIMESTAMPNS)
+#define SCM_WIFI_STATUS  SYMBOLIC(SCM_WIFI_STATUS)
+
+#endif /* COSMOPOLITAN_LIBC_SYSV_CONSTS_SCM_H_ */