LowerTypeTests: Teach the pass to respect global alignments.

LowerTypeTests: Teach the pass to respect global alignments.

We were previously ignoring alignment entirely when combining globals
together in this pass. There are two main things that we need to do here:
add additional padding before each global to meet the alignment requirements,
and set the combined global's alignment to the maximum of all of the original
globals' alignments.

Since we now need to calculate layout as we go anyway, use the calculated
layout to produce GlobalLayout instead of using StructLayout.

Differential Revision: https://reviews.llvm.org/D65033

llvm-svn: 366722