Temporarily revert r158087.

This patch causes problems when both dynamic stack realignment and
dynamic allocas combine in the same function. With this patch, we no
longer build the epilog correctly, and silently restore registers from
the wrong position in the stack.

Thanks to Matt for tracking this down, and getting at least an initial
test case to Chad. I'm going to try to check a variation of that test
case in so we can easily track the fixes required.

llvm-svn: 158654