[X86] Add test cases showing incorrect setting of nofpexcept flag due to CSE...

[X86] Add test cases showing incorrect setting of nofpexcept flag due to CSE occuring during SelectionDAG creation.

These tests generate two nodes that are identical except for the
metadata that indicates their exception behavior. The nodes get
CSEd by SelectionDAG, but the nofpexcept flag is being set based
only on the fpexcept.ignore node being created last.

We need to detect this case and intersect the flags similar to
what is already done with fast math flags.