rs6000: Rework vector float comparison in rs6000_emit_vector_compare - p2

rs6000: Rework vector float comparison in rs6000_emit_vector_compare - p2

All kinds of vector float comparison operators have been
supported in a rtl comparison pattern as vector.md, we can
just emit an rtx comparison insn with the given comparison
operator in function rs6000_emit_vector_compare instead of
checking and handling the reverse condition cases.

This is part 2, it further checks for comparison opeators
NE/UNLE/UNLT.  In rs6000_emit_vector_compare, they are
handled with reversed code which is queried from function
reverse_condition_maybe_unordered and inverting with
one_cmpl_optab.  It's the same as what we have in vector.md:

; ne(a,b)   = ~eq(a,b)
; unle(a,b) = ~gt(a,b)
; unlt(a,b) = ~ge(a,b)

The operators on the right side have been supported in part 1.
This patch should not have any functionality change too.

gcc/ChangeLog:

	* config/rs6000/rs6000.cc (rs6000_emit_vector_compare): Emit rtx
	comparison for operators NE/UNLE/UNLT of MODE_VECTOR_FLOAT directly.