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/linkat.c

@@ -40,7 +40,6 @@
 int linkat(int olddirfd, const char *oldpath, int newdirfd, const char *newpath,
            int flags) {
   int rc;
-  char buf[2][12];
   if (IsAsan() &&
       (!__asan_is_valid(oldpath, 1) || !__asan_is_valid(newpath, 1))) {
     rc = efault();
@@ -53,8 +52,7 @@ int linkat(int olddirfd, const char *oldpath, int newdirfd, const char *newpath,
   } else {
     rc = sys_linkat_nt(olddirfd, oldpath, newdirfd, newpath);
   }
-  STRACE("linkat(%s, %#s, %s, %#s, %#b) → %d% m",
-         DescribeDirfd(buf[0], olddirfd), oldpath,
-         DescribeDirfd(buf[1], newdirfd), newpath, flags, rc);
+  STRACE("linkat(%s, %#s, %s, %#s, %#b) → %d% m", DescribeDirfd(olddirfd),
+         oldpath, DescribeDirfd(newdirfd), newpath, flags, rc);
   return rc;
 }