[SPARC] Fix stupid oversight in stack realignment support.

[SPARC] Fix stupid oversight in stack realignment support.

If you're going to realign %sp to get object alignment properly (which
the code does), and stack offsets and alignments are calculated going
down from %fp (which they are), then the total stack size had better
be a multiple of the alignment. LLVM did indeed ensure that.

And then, after aligning, the sparc frame code added 96 (for sparcv8)
to the frame size, making any requested alignment of 64-bytes or
higher *guaranteed* to be misaligned. The test case added with r245668
even tests this exact scenario, and asserted the incorrect behavior,
which I somehow failed to notice. D'oh.

This change fixes the frame lowering code to align the stack size
*after* adding the spill area, instead.

Differential Revision: http://reviews.llvm.org/D12349

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246042 91177308-0d34-0410-b5e6-96231b3b80d8