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/calls/issymlink-nt.c

@@ -18,6 +18,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
 #include "libc/calls/internal.h"
+#include "libc/errno.h"
 #include "libc/nt/enum/fileflagandattributes.h"
 #include "libc/nt/files.h"
 
@@ -25,12 +26,15 @@
  * Returns true if file exists and is a symbolic link on Windows NT.
  */
 bool issymlink_nt(const char *path) {
+  int e;
   uint32_t x;
   char16_t path16[PATH_MAX];
+  e = errno;
   if (__mkntpath(path, path16) == -1) return -1;
   if ((x = GetFileAttributes(path16)) != -1u) {
     return !!(x & kNtFileAttributeReparsePoint);
   } else {
+    errno = e;
     return false;
   }
 }