Make improvements

- Polyfill readlink("foo/") dir check on Windows
- Support asynchronous signal delivery on Windows
- Restore Windows Console from execve() daisy chain
- Work around bug in AARCH64 Optimized Routines memcmp()
- Disable unbourne.com shell completion on Windows for now
- Don't always set virtual terminal input state on console
- Remove Musl Libc's unusual preservation of realpath("//")
- Make realpath() strongly link malloc() to pass configure test
- Delete cosh.com shell, now that unbourne.com works on Windows!

examples/ttyinfo.c

@@ -55,7 +55,7 @@ int rawmode(void) {
   static bool once;
   struct termios t;
   if (!once) {
-    if (tcgetattr(1, &oldterm)) {
+    if (!tcgetattr(1, &oldterm)) {
       atexit(restoretty);
     } else {
       perror("tcgetattr");