Revert "Move internal usages of `alignof`/`__alignof` to use `_LIBCPP_ALIGNOF`. "

This reverts commit 087f065cb0c7463f521a62599884493aaee2ea12.

The tests were failing on 32 bit builds, and I don't have time
to clean them up right now. I'll recommit tomorrow with fixed tests.

llvm-svn: 347816
diff --git a/libcxx/include/experimental/coroutine b/libcxx/include/experimental/coroutine
index 7cb39b8..1eb224a 100644
--- a/libcxx/include/experimental/coroutine
+++ b/libcxx/include/experimental/coroutine
@@ -214,7 +214,7 @@
     _LIBCPP_INLINE_VISIBILITY
     _Promise& promise() const {
         return *static_cast<_Promise*>(
-            __builtin_coro_promise(this->__handle_, _LIBCPP_ALIGNOF(_Promise), false));
+            __builtin_coro_promise(this->__handle_, __alignof(_Promise), false));
     }
 
 public:
@@ -254,7 +254,7 @@
         coroutine_handle __tmp;
         __tmp.__handle_ = __builtin_coro_promise(
             _VSTD::addressof(const_cast<_RawPromise&>(__promise)),
-             _LIBCPP_ALIGNOF(_Promise), true);
+             __alignof(_Promise), true);
         return __tmp;
     }
 };
@@ -272,7 +272,7 @@
   _LIBCPP_INLINE_VISIBILITY
   _Promise& promise() const {
     return *static_cast<_Promise*>(
-      __builtin_coro_promise(this->__handle_, _LIBCPP_ALIGNOF(_Promise), false));
+      __builtin_coro_promise(this->__handle_, __alignof(_Promise), false));
   }
 
   _LIBCPP_CONSTEXPR explicit operator bool() const _NOEXCEPT { return true; }