[libcxx] [test] D27022: Fix MSVC warning C4389 "signed/unsigned mismatch", part 9/12.

Add static_cast<std::size_t> to more comparisons. (Performed manually, unlike part 8/12.)

Also, include <cstddef> when it wasn't already being included.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@288746 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/numerics/numarray/valarray.range/end_const.pass.cpp

@@ -17,6 +17,7 @@
 
 #include <valarray>
 #include <cassert>
+#include <cstddef>
 
 int main()
 {
@@ -26,6 +27,6 @@ int main()
         const unsigned N = sizeof(a)/sizeof(a[0]);
         const std::valarray<T> v(a, N);
         assert(v[v.size()-1] == 5);
-        assert(end(v) - begin(v) == v.size());
+        assert(static_cast<std::size_t>(end(v) - begin(v)) == v.size());
     }
 }