[fusl] Don't syscall(SYS_ioctl, ...) in stdio

fusl/src/stdio/__stdout_write.c

Index: fusl/src/stdio/__stdout_write.c
diff --git a/fusl/src/stdio/__stdout_write.c b/fusl/src/stdio/__stdout_write.c
index f17b9a554ada2bcb82849aaf24ce25f26145ec6d..5cbe7799d401dd0c65f6c645a1ba68e677be9a01 100644
--- a/fusl/src/stdio/__stdout_write.c
+++ b/fusl/src/stdio/__stdout_write.c
@@ -1,10 +1,9 @@
 #include "stdio_impl.h"
-#include <sys/ioctl.h>
+#include <unistd.h>
 
 size_t __stdout_write(FILE* f, const unsigned char* buf, size_t len) {
-  struct winsize wsz;
   f->write = __stdio_write;
-  if (!(f->flags & F_SVB) && __syscall(SYS_ioctl, f->fd, TIOCGWINSZ, &wsz))
+  if (!(f->flags & F_SVB) && !isatty(f->fd))
     f->lbf = -1;
   return __stdio_write(f, buf, len);
 }