[libcxx] [test] Narrow down an XFAIL for clang-cl configurations

[mstorsjo]

Summary

This test only fails on x86_64 clang-cl, not for i386.

(The root cause is still not explored, thus the FIXME is still
relevant.)

libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/copy_move.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // FIXME: In MSVC mode, even "std::function<int(int)> f(aref);" causes
 // allocations.
-// XFAIL: msvc && stdlib=libc++
+// XFAIL: target=x86_64-pc-windows-msvc && stdlib=libc++
 
 // <functional>
 
 // class function<R(ArgTypes...)>
 
 // function(const function&  f);
 // function(function&& f); // noexcept in C++20