DataLayout should use itself when calculating the size of a vector.

DataLayout should use itself when calculating the size of a vector.

This is important for vectors of pointers because only DataLayout,
not the underlying vector type, knows how to calculate the size
of the pointers in the vector. Fixes PR14138.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166401 91177308-0d34-0410-b5e6-96231b3b80d8