Implement isatty

tests/unistd/isatty.c

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main() {
+    // 1 is stdout
+    if (isatty(1)) {
+        puts("'Tis a tty :D");
+    } else {
+        puts("Whatever a tty is, it's not me");
+    }
+}