[libcxx] [test] Improve portability of random_device tests.

[STL_MSFT]

Summary

Improve portability of random_device tests.

These tests were failing for MSVC, because we ignore the token (as permitted by the Standard). Marking the asserts as libcxx-specific is all we need.

[EricWF]

r272746.

test/std/numerics/rand/rand.device/ctor.pass.cpp

 #include <random>
 #include <system_error>
 #include <cassert>
 
 #if !defined(_WIN32)
 #include <unistd.h>
 #endif
 
+#include "test_macros.h"
+
 
 bool is_valid_random_device(const std::string &token) {
 #if defined(_LIBCPP_USING_DEV_RANDOM)
   // Not an exhaustive list: they're the only tokens that are tested below.
   return token == "/dev/urandom" || token == "/dev/random";
 #else
   return token == "/dev/urandom";
 #endif
 }
 
 void check_random_device_valid(const std::string &token) {
   std::random_device r(token);
 }
 
 void check_random_device_invalid(const std::string &token) {
   try {
     std::random_device r(token);
-    assert(false);
+    LIBCPP_ASSERT(false);
   } catch (const std::system_error&) {
   }
 }
 
 
 int main() {
   {
     std::random_device r;

test/std/numerics/rand/rand.device/eval.pass.cpp

 
 // class random_device;
 
 // result_type operator()();
 
 #include <random>
 #include <cassert>
 
+#include "test_macros.h"
+
 int main()
 {
     {
         std::random_device r;
         std::random_device::result_type e = r();
     }
 
     try
     {
         std::random_device r("/dev/null");
         r();
-        assert(false);
+        LIBCPP_ASSERT(false);
     }
     catch (const std::system_error&)
     {
     }
 }