[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.

Fixes D45594.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@329976 91177308-0d34-0410-b5e6-96231b3b80d8

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

@@ -22,6 +22,10 @@
 #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