[SDAG] Optimize unordered comparison in soft-float mode (patch by Anton Nadolskiy)

[SDAG] Optimize unordered comparison in soft-float mode (patch by Anton Nadolskiy)

Current implementation handles unordered comparison poorly in soft-float mode.
Consider (a ULE b) which is a <= b. It is lowered to (ledf2(a, b) <= 0 || unorddf2(a, b) != 0) (in general). We can do better job by lowering it to (__gtdf2(a, b) <= 0).
Such replacement is true for other CMP's (ult, ugt, uge). In general, we just call same function as for ordered case but negate comparison against zero.
Differential Revision: http://reviews.llvm.org/D10804

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242280 91177308-0d34-0410-b5e6-96231b3b80d8