Newlib: implement locks

* Dynamically allocate arc4random data. Saves about 1k off the bss.

libc/xtensa-lx106-elf/include/machine/_arc4random.h

@@ -1 +1,32 @@
-/* Use default implementation, see arc4random.h */
+/*
+ * Copyright (c) 2017
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+void _arc4random_getentropy_fail(void);
+
+#define _ARC4RANDOM_DATA
+
+#define _ARC4RANDOM_GETENTROPY_FAIL() _arc4random_getentropy_fail()
+
+#define _ARC4RANDOM_ALLOCATE(rsp, rsxp)  \
+  do { *rsp = malloc(sizeof(**rsp));     \
+       *rsxp = malloc(sizeof(**rsxp)); } \
+  while (0)
+
+__END_DECLS