Rewrite the TrailingObjects template to provide two new features:

Rewrite the TrailingObjects template to provide two new features:

 - Automatic alignment of the base type for the alignment requirements
   of the trailing types.

 - Support for an arbitrary numbers of trailing types, instead of only
   1 or 2, by using a variadic template implementation.

Upcoming commits to clang will take advantage of both of these features.

Differential Revision: http://reviews.llvm.org/D12439

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256054 91177308-0d34-0410-b5e6-96231b3b80d8