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/calls/unlinkat.c

@@ -40,7 +40,6 @@
  */
 int unlinkat(int dirfd, const char *path, int flags) {
   int rc;
-  char buf[12];
   if (IsAsan() && !__asan_is_valid(path, 1)) {
     rc = efault();
   } else if (weaken(__zipos_notat) && (rc = __zipos_notat(dirfd, path)) == -1) {
@@ -50,7 +49,7 @@ int unlinkat(int dirfd, const char *path, int flags) {
   } else {
     rc = sys_unlinkat_nt(dirfd, path, flags);
   }
-  STRACE("unlinkat(%s, %#s, %#b) → %d% m", DescribeDirfd(buf, dirfd), path,
-         flags, rc);
+  STRACE("unlinkat(%s, %#s, %#b) → %d% m", DescribeDirfd(dirfd), path, flags,
+         rc);
   return rc;
 }