[Sema] Fix bug in TypeLocBuilder::pushImpl

The code in TypeLocBuilder::pushImpl wasn't correctly handling the case
where an element that has an 8-byte alignment was being pushed.

I plan to follow up with a patch to remove redundancies and simplify the
function.

rdar://problem/23838912

Differential Revision: http://reviews.llvm.org/D16843

llvm-svn: 261260