Add pseudoteletypewriter to emulator

https://justine.storage.googleapis.com/emulator628.mp4

tool/build/lib/buffer.c

@@ -17,6 +17,7 @@
 │ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
 │ 02110-1301 USA                                                               │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "dsp/tty/tty.h"
 #include "libc/alg/arraylist2.h"
 #include "libc/calls/calls.h"
 #include "libc/fmt/fmt.h"
@@ -57,12 +58,5 @@ void AppendFmt(struct Buffer *b, const char *fmt, ...) {
  * Writes buffer until completion, interrupt, or error occurs.
  */
 ssize_t WriteBuffer(struct Buffer *b, int fd) {
-  size_t i;
-  ssize_t rc;
-  for (i = 0; i < b->i; i += rc) {
-    if ((rc = write(fd, b->p + i, b->i - i)) == -1) {
-      return -1;
-    }
-  }
-  return i;
+  return ttywrite(fd, b->p, b->i);
 }