fix sign comparison warnings

llvm-svn: 290469
diff --git a/libcxx/include/random b/libcxx/include/random
index 794bf7b..4e11f9e 100644
--- a/libcxx/include/random
+++ b/libcxx/include/random
@@ -2817,6 +2817,7 @@
 
     static_assert(  0 <  __r, "discard_block_engine invalid parameters");
     static_assert(__r <= __p, "discard_block_engine invalid parameters");
+    static_assert(__r <= INT_MAX, "discard_block_engine invalid parameters");
 public:
     // types
     typedef typename _Engine::result_type result_type;
@@ -2918,7 +2919,7 @@
 typename discard_block_engine<_Engine, __p, __r>::result_type
 discard_block_engine<_Engine, __p, __r>::operator()()
 {
-    if (__n_ >= __r)
+    if (__n_ >= static_cast<int>(__r))
     {
         __e_.discard(__p - __r);
         __n_ = 0;