Make fixes and improvements

- Introduce __assert_disable global
- Improve strsignal() thread safety
- Make system call tracing thread safe
- Fix SO_RCVTIMEO / SO_SNDTIMEO on Windows
- Refactor DescribeFoo() functions into one place
- Fix fork() on Windows when TLS and MAP_STACK exist
- Round upwards in setsockopt(SO_RCVTIMEO) on Windows
- Disable futexes on OpenBSD which seem extremely broken
- Implement a better kludge for monotonic time on Windows

libc/sock/struct/msghdr.h

@@ -0,0 +1,19 @@
+#ifndef COSMOPOLITAN_LIBC_SOCK_STRUCT_MSGHDR_H_
+#define COSMOPOLITAN_LIBC_SOCK_STRUCT_MSGHDR_H_
+#include "libc/calls/struct/iovec.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+struct msghdr {            /* Linux+NT ABI */
+  void *msg_name;          /* optional address */
+  uint32_t msg_namelen;    /* size of msg_name */
+  struct iovec *msg_iov;   /* scatter/gather array */
+  uint64_t msg_iovlen;     /* iovec count */
+  void *msg_control;       /* credentials and stuff */
+  uint64_t msg_controllen; /* size of msg_control */
+  uint32_t msg_flags;      /* MSG_XXX */
+};
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_SOCK_STRUCT_MSGHDR_H_ */