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/nt/kernel32/CancelIoEx.S

@@ -1,2 +1,18 @@
 #include "libc/nt/codegen.h"
 .imp	kernel32,__imp_CancelIoEx,CancelIoEx
+
+	.text.windows
+        .ftrace1
+CancelIoEx:
+        .ftrace2
+#ifdef __x86_64__
+	push	%rbp
+	mov	%rsp,%rbp
+	mov	__imp_CancelIoEx(%rip),%rax
+	jmp	__sysv2nt
+#elif defined(__aarch64__)
+	mov	x0,#0
+	ret
+#endif
+	.endfn	CancelIoEx,globl
+	.previous