DwarfCompileUnit: Push DIDescriptors through a getDIE/insertDIE

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194875 91177308-0d34-0410-b5e6-96231b3b80d8
LoopVectorizer: Use abi alignment for accesses with no alignment

When we vectorize a scalar access with no alignment specified, we have to set
the target's abi alignment of the scalar access on the vectorized access.
Using the same alignment of zero would be wrong because most targets will have a
bigger abi alignment for vector types.

This probably fixes PR17878.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194876 91177308-0d34-0410-b5e6-96231b3b80d8