[libcxx] [test] Silence MSVC warning C4146.

[STL_MSFT]

Summary

[libcxx] [test] Silence MSVC warning C4146.

This test code triggers the MSVC warning:

"unary minus operator applied to unsigned type, result still unsigned"

Although it would be possible to change the test code to avoid
this warning, I have chosen to simply silence it.

[EricWF]

This would have been fine for post-commit review.

[STL_MSFT]

Committed, with a follow-up to use the C1XX macro.

test/std/localization/locale.categories/category.numeric/locale.num.get/facet.num.get.members/test_neg_one.pass.cpp

 #include <locale>
 #include <ios>
 #include <cassert>
 #include <streambuf>
 #include <sstream>
 #include <iostream>
 #include "test_iterators.h"
 
+#ifdef _MSC_VER
+#pragma warning(disable: 4146) // unary minus operator applied to unsigned type, result still unsigned
+#endif
+
 typedef std::num_get<char, input_iterator<const char*> > F;
 
 class my_facet
     : public F
 {
 public:
     explicit my_facet(std::size_t refs = 0)
         : F(refs) {}