Improve system call support on NT

- Improve i/o perf on New Technology
- Code cleanup on read() for New Technology
- Fix bad bug with dup() of socket on New Technology
- Clean up some more strace errors on New Technology

libc/intrin/exit.greg.c

@@ -37,7 +37,7 @@
 privileged noinstrument noasan noubsan wontreturn void _Exit(int exitcode) {
   int i;
   STRACE("_Exit(%d)", exitcode);
-  if ((!IsWindows() && !IsMetal()) || (IsMetal() && IsGenuineCosmo())) {
+  if (!IsWindows() && !IsMetal()) {
     asm volatile("syscall"
                  : /* no outputs */
                  : "a"(__NR_exit_group), "D"(exitcode)