Address part A of #982: $Global will use std140 instead of HLSL offsets.

From comment about this:
Adjust alignment for HLSL rules
TODO: make this consistent in early phases of code: adjusting this late means inconsistencies with earlier code, which for reflection is an issue.
Until reflection is brought in sync with these adjustments, don't apply to $Global,
which is the most likely to rely on reflection, and least likely to rely
implicit layouts.