Lower the default alignment on ASTContext's operator new.

Lower the default alignment on ASTContext's operator new.

It was documented as 8 and operator new[] defaults to 8, but the normal
operator new was never updated and happily wasted bytes on every other
allocation.

We still have to allocate all Types with 16 byte alignment, update the
allocation calls for Types that were missing explicit alignment.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@233922 91177308-0d34-0410-b5e6-96231b3b80d8