[libc++] Use _Alignas instead of __attribute__((__aligned__()))

[philnik]

• Fix CI

libcxx/include/__config

 #    define _LIBCPP_NO_CFI __attribute__((__no_sanitize__("cfi")))
 #  else
 #    define _LIBCPP_NO_CFI
 #  endif
 
 #  ifndef _LIBCPP_CXX03_LANG
 
 #    define _LIBCPP_ALIGNOF(_Tp) alignof(_Tp)
-#    define _ALIGNAS_TYPE(x) alignas(x)
-#    define _ALIGNAS(x) alignas(x)
+#    define _ALIGNAS(...) alignas(__VA_ARGS__)
 #    define _LIBCPP_NORETURN [[noreturn]]
 #    define _NOEXCEPT noexcept
 #    define _NOEXCEPT_(x) noexcept(x)
 
 #  else
 
 #    define _LIBCPP_ALIGNOF(_Tp) _Alignof(_Tp)
-#    define _ALIGNAS_TYPE(x) __attribute__((__aligned__(_LIBCPP_ALIGNOF(x))))
-#    define _ALIGNAS(x) __attribute__((__aligned__(x)))
+#    define _ALIGNAS(...) _Alignas(__VA_ARGS__)
 #    define _LIBCPP_NORETURN __attribute__((noreturn))
 #    define _LIBCPP_HAS_NO_NOEXCEPT
 #    define nullptr __nullptr
 #    define _NOEXCEPT throw()
 #    define _NOEXCEPT_(x)
 
 typedef __char16_t char16_t;
 typedef __char32_t char32_t;

libcxx/include/__memory/shared_ptr.h

#endif
     // through `std::allocate_shared` and `std::make_shared`.
     //
     // In previous versions of the library, we used a compressed pair to store
     // both the _Alloc and the _Tp. This implies using EBO, which is incompatible
     // with Allocator construction for _Tp. To allow implementing P0674 in C++20,
     // we now use a properly aligned char buffer while making sure that we maintain
     // the same layout that we had when we used a compressed pair.
     using _CompressedPair = __compressed_pair<_Alloc, _Tp>;
-    struct _ALIGNAS_TYPE(_CompressedPair) _Storage {
+    struct _ALIGNAS(_CompressedPair) _Storage {
         char __blob_[sizeof(_CompressedPair)];
 
         _LIBCPP_HIDE_FROM_ABI explicit _Storage(_Alloc&& __a) {
             ::new ((void*)__get_alloc()) _Alloc(_VSTD::move(__a));
         }
         _LIBCPP_HIDE_FROM_ABI ~_Storage() {
             __get_alloc()->~_Alloc();
         }

libcxx/include/array

struct _LIBCPP_TEMPLATE_VIS array<_Tp, 0>
     typedef ptrdiff_t                             difference_type;
     typedef _VSTD::reverse_iterator<iterator>       reverse_iterator;
     typedef _VSTD::reverse_iterator<const_iterator> const_reverse_iterator;
 
     typedef typename conditional<is_const<_Tp>::value, const char,
                                 char>::type _CharType;
 
     struct  _ArrayInStructT { _Tp __data_[1]; };
-    _ALIGNAS_TYPE(_ArrayInStructT) _CharType __elems_[sizeof(_ArrayInStructT)];
+    _ALIGNAS(_ArrayInStructT) _CharType __elems_[sizeof(_ArrayInStructT)];
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
     value_type* data() _NOEXCEPT {return nullptr;}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
     const value_type* data() const _NOEXCEPT {return nullptr;}
 
     // No explicit construct/copy/destroy for aggregate type
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17

libcxx/test/support/test_macros.h

 # define TEST_NOEXCEPT_FALSE noexcept(false)
 # define TEST_NOEXCEPT_COND(...) noexcept(__VA_ARGS__)
 #else
 #   if defined(TEST_COMPILER_CLANG)
 #    define TEST_ALIGNOF(...) _Alignof(__VA_ARGS__)
 #   else
 #    define TEST_ALIGNOF(...) __alignof(__VA_ARGS__)
 #   endif
-# define TEST_ALIGNAS(...) __attribute__((__aligned__(__VA_ARGS__)))
+# define TEST_ALIGNAS(...) _Alignas(__VA_ARGS__)
 # define TEST_CONSTEXPR
 # define TEST_NOEXCEPT throw()
 # define TEST_NOEXCEPT_FALSE
 # define TEST_NOEXCEPT_COND(...)
 #endif
 
 #if TEST_STD_VER >= 11
 # define TEST_THROW_SPEC(...)