[X86] Determine if we have an OpaqueSPAdjustment earlier

We queried hasFP before we hit ExpandISelPseudos.  ExpandISelPseudos
manipulated state that hasFP relied on, potentially changing the result
after it has been queried elsewhere.

While I am not aware of any particular bug due to this state of affairs,
it seems best to avoid it entirely by changing the state during DAG
construction.

llvm-svn: 256849