Remove usages of _LIBCPP_MSVC which is never defined

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@302736 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/function.objects/func.not_fn/not_fn.pass.cpp

@@ -416,7 +416,7 @@ void throws_in_constructor_test()
       ThrowsOnCopy() = default;
       bool operator()() const {
         assert(false);
-#if defined(_LIBCPP_MSVC)
+#if defined(TEST_COMPILER_C1XX)
         __assume(0);
 #else
         __builtin_unreachable();