io.c: sys/wait.h

* io.c: BSDs need sys/wait.h for WNOHANG.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51809 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -96,6 +96,10 @@
 #include <sys/uio.h>
 #endif
 
+#ifdef HAVE_SYS_WAIT_H
+# include <sys/wait.h>		/* for WNOHANG on BSD */
+#endif
+
 #if defined(__BEOS__) || defined(__HAIKU__)
 # ifndef NOFILE
 #  define NOFILE (OPEN_MAX)