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/intrin/getfileattributes.c

@@ -36,6 +36,6 @@ textwindows uint32_t GetFileAttributes(const char16_t *lpPathName) {
   flags = __imp_GetFileAttributesW(lpPathName);
   if (flags == -1u) __winerr();
   NTTRACE("GetFileAttributes(%#hs) → %s% m", lpPathName,
-          DescribeNtFileFlagsAndAttributes(flags));
+          DescribeNtFileFlagAttr(flags));
   return flags;
 }