[ADT] PutPointer() in FoldingSet looks strange.

Hi.

Most probably its a bug. Because we use some random garbage for hashing instead of a real pointer value. Also, we put 16 bytes instead of 8 byte of pointer size which is strange too. Here is my fix http://reviews.llvm.org/D17377 Please, review it and commit if all is fine because I have no commit rights. Thanks for your time.