[libcxx] random_device, use arc4random() on Solaris

Reviewed By: ldionne

Differential Revision: https://reviews.llvm.org/D125068

Author: brad0

libcxx/docs/ReleaseNotes.rst

@@ -104,8 +104,8 @@ ABI Changes
   ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` will not be honoured anymore and there
   will be no way to opt back into the C++03 emulation of ``std::nullptr_t``.
 
-- On FreeBSD, NetBSD and DragonFlyBSD, ``std::random_device`` is now implemented on top of
-  ``arc4random()`` instead of reading from ``/dev/urandom``. Any implementation-defined
+- On FreeBSD, NetBSD, DragonFlyBSD and Solaris, ``std::random_device`` is now implemented on
+  top of ``arc4random()`` instead of reading from ``/dev/urandom``. Any implementation-defined
   token used when constructing a ``std::random_device`` will now be ignored instead of
   interpreted as a file to read entropy from.
 

libcxx/include/__config

@@ -351,7 +351,7 @@
 //      When this option is used, the token passed to `std::random_device`'s
 //      constructor *must* be "/dev/urandom" -- anything else is an error.
 #if defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
-    defined(__OpenBSD__) || defined(__DragonFly__)
+    defined(__OpenBSD__) || defined(__DragonFly__) || defined(__sun__)
 #  define _LIBCPP_USING_ARC4_RANDOM
 #elif defined(__wasi__)
 #  define _LIBCPP_USING_GETENTROPY