Add __stdio_write.c from musl c library
Added F_STDOUT flag and changed stdout to use __stdio_write

The F_STDOUT flag is used to determine if the FILE is stdout,
if so, then system_stdout_writev is called to write data
Removed __stdout_write.c

No longer needed, stdout uses __stdio_write to write output
stdout now uses __stdio_write

the allows stdout to use scatter gather buffering