[libcxx] [test] Fix size_t-to-int truncation warnings in syserr.hash.

[STL_MSFT]

Summary

[libcxx] [test] Fix size_t-to-int truncation warnings in syserr.hash.

After r289363, these tests were triggering MSVC x64 warning C4267
"conversion from 'size_t' to 'int', possible loss of data" by taking 0, 2, and 10
as std::size_t, then constructing error_code(int, const error_category&) or
error_condition(int, const error_category&) from that (N4618 19.5.3.2
[syserr.errcode.constructors]/3, 19.5.4.2 [syserr.errcondition.constructors]/3).

The fix is simple: take these ints as int, pass them to the int-taking
constructor, and perform a value-preserving static_cast<std::size_t>
when comparing them to std::size_t result.

[STL_MSFT]

This regressed after r289363, adding that to the notes. Also, the error_condition test was equally affected, which I initially missed because we haven't implemented LWG 2686 "Why is std::hash specialized for error_code, but not error_condition?" yet (so the test is disabled for us).

test/std/diagnostics/syserr/syserr.hash/error_code.pass.cpp

 
 #include <system_error>
 #include <cassert>
 #include <type_traits>
 
 #include "test_macros.h"
 
 void
-test(std::size_t i)
+test(int i)
 {
     typedef std::error_code T;
     typedef std::hash<T> H;
     static_assert((std::is_same<H::argument_type, T>::value), "" );
     static_assert((std::is_same<H::result_type, std::size_t>::value), "" );
     H h;
     T ec(i, std::system_category());
     const std::size_t result = h(ec);
-    LIBCPP_ASSERT(result == i);
+    LIBCPP_ASSERT(result == static_cast<std::size_t>(i));
     ((void)result); // Prevent unused warning
 }
 
 int main()
 {
     test(0);
     test(2);
     test(10);
 }

test/std/diagnostics/syserr/syserr.hash/error_condition.pass.cpp

 
 #include <system_error>
 #include <cassert>
 #include <type_traits>
 
 #include "test_macros.h"
 
 void
-test(std::size_t i)
+test(int i)
 {
     typedef std::error_condition T;
     typedef std::hash<T> H;
     static_assert((std::is_same<H::argument_type, T>::value), "" );
     static_assert((std::is_same<H::result_type, std::size_t>::value), "" );
     H h;
     T ec(i, std::system_category());
     const std::size_t result = h(ec);
-    LIBCPP_ASSERT(result == i);
+    LIBCPP_ASSERT(result == static_cast<std::size_t>(i));
     ((void)result); // Prevent unused warning
 }
 
 int main()
 {
     test(0);
     test(2);
     test(10);
 }