runtime: Fix typo in dup3 fallback implementation.

From Uros Bizjak.

From-SVN: r203820
diff --git a/libgo/runtime/go-nosys.c b/libgo/runtime/go-nosys.c
index f389dbe..0a94de0 100644
--- a/libgo/runtime/go-nosys.c
+++ b/libgo/runtime/go-nosys.c
@@ -47,7 +47,7 @@
 int
 dup3 (int oldfd __attribute__ ((unused)),
       int newfd __attribute__ ((unused)),
-      int flags __attribtue__ ((unused)))
+      int flags __attribute__ ((unused)))
 {
   errno = ENOSYS;
   return -1;