Allow machine-dependent arc4 locking

newlib:
	* libc/stdlib/arc4random.h: Remove Cygwin-specific locking code.
	Conditionalize arc4 locking.  Check for _ARC4_LOCK_INIT being
	undefined to fall back to default implementation.

cygwin:
	* include/machine/_arc4random.h: New file.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/include/machine/_arc4random.h

@@ -0,0 +1,30 @@
+/* machine/_arc4random.h
+
+   Copyright 2016 Red Hat, Inc.
+
+This file is part of Cygwin.
+
+This software is a copyrighted work licensed under the terms of the
+Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
+details. */
+
+#ifndef _MACHINE_ARC4RANDOM_H
+#define _MACHINE_ARC4RANDOM_H
+
+extern int __isthreaded;
+
+#define _ARC4_LOCK_INIT	__LOCK_INIT(static, _arc4random_mutex);
+
+#define _ARC4_LOCK()				\
+        do {					\
+	  if (__isthreaded)			\
+	    __lock_acquire (_arc4random_mutex);	\
+        } while (0)
+
+#define _ARC4_UNLOCK()				\
+        do {					\
+	  if (__isthreaded)			\
+	    __lock_release (_arc4random_mutex);	\
+        } while (0)
+
+#endif /* _MACHINE_ARC4RANDOM_H */