Improve Windows Console I/O

- Blocking read operations on the Windows Console can now EINTR
- Blocking read operations on Windows pipes now EINTR more reliably
- setitimer() will no longer be inherited across fork() on Windows
- It's now possible to use ECHO when the console is in raw mode
- The ECHOCTL flag now works correctly on the Windows Console
- The ICRNL flag now works correctly on the Windows Console
- pread() and pwrite() will now raise ESPIPE on Windows
- Opening /dev/tty on Windows is improved (untested)
- Overlapped I/O is now implemented in a better way

libc/calls/struct/fd.internal.h

@@ -13,13 +13,19 @@ COSMOPOLITAN_C_START_
 #define kFdEpoll    7
 #define kFdReserved 8
 
+#define kFdTtyEchoing 1 /* read()→write() (ECHO && !ICANON) */
+#define kFdTtyEchoRaw 2 /* don't ^X visualize control codes */
+#define kFdTtyMunging 4 /* enable input / output remappings */
+#define kFdTtyNoCr2Nl 8 /* don't map \r → \n (a.k.a !ICRNL) */
+
 struct Fd {
-  int kind;
+  char kind;
+  bool zombie;
+  char ttymagic;
   unsigned flags;
   unsigned mode;
   int64_t handle;
   int64_t extra;
-  bool zombie;
 };
 
 struct Fds {