[RISCV] Add test cases to show where we inverted a fp setcc and introduced an extra xori.

In these tests we had (sub C, (seteq X, Y)) which we converted to
the (add (setne X, Y), C-1). We don't have a FNE compare instruction
so this created an XORI to invert an FEQ instruction.

This might be a good idea since it can save a constant materialization,
but does not appear to be the intention of the original patch.