[libc++][PSTL] Fix nasty macros test

libcxx/include/__pstl/internal/execution_defs.h

 
 // 2.8, Execution policy objects
 constexpr sequenced_policy seq{};
 constexpr parallel_policy par{};
 constexpr parallel_unsequenced_policy par_unseq{};
 constexpr unsequenced_policy unseq{};
 
 // 2.3, Execution policy type trait
-template <class T>
+template <class>
 struct is_execution_policy : std::false_type {};
 
 template <>
 struct is_execution_policy<__pstl::execution::sequenced_policy> : std::true_type {};
 template <>
 struct is_execution_policy<__pstl::execution::parallel_policy> : std::true_type {};
 template <>
 struct is_execution_policy<__pstl::execution::parallel_unsequenced_policy> : std::true_type {};
 template <>
 struct is_execution_policy<__pstl::execution::unsequenced_policy> : std::true_type {};
 
 #if defined(_PSTL_CPP14_VARIABLE_TEMPLATES_PRESENT)
-template <class T>
-constexpr bool is_execution_policy_v = __pstl::execution::is_execution_policy<T>::value;
+template <class _Tp>
+constexpr bool is_execution_policy_v = __pstl::execution::is_execution_policy<_Tp>::value;
 #endif
 
 } // namespace v1
 } // namespace execution
 
 namespace __internal {
-template <class ExecPolicy, class T>
+template <class _ExecPolicy, class _Tp>
 using __enable_if_execution_policy =
-    typename std::enable_if<__pstl::execution::is_execution_policy<typename std::decay<ExecPolicy>::type>::value,
-                            T>::type;
+    typename std::enable_if<__pstl::execution::is_execution_policy<typename std::decay<_ExecPolicy>::type>::value,
+                            _Tp>::type;
 
 template <class _IsVector>
 struct __serial_tag;
 template <class _IsVector>
 struct __parallel_tag;
 
 } // namespace __internal
 
 } // namespace __pstl
 
 #endif /* _PSTL_EXECUTION_POLICY_DEFS_H */

libcxx/test/libcxx/nasty_macros.compile.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
 //
 //===----------------------------------------------------------------------===//
 
 // Test that headers are not tripped up by the surrounding code defining various
 // alphabetic macros.
 
-// FIXME: This should pass with the PSTL enabled
-// XFAIL: with-pstl
-
 // Prevent <ext/hash_map> from generating deprecated warnings for this test.
 #if defined(__DEPRECATED)
 #    undef __DEPRECATED
 #endif
 
 #define NASTY_MACRO This should not be expanded!!!
 
 // libc++ does not use single-letter names as a matter of principle.