Fix SIMD float comparison encoding (#1285)

The Intel manual uses `CMPNLT` and `CMPNLE` to denote not-less-than and not-less-than-or-equals. These were translated previously to `FloatCC::GreaterThan` and `FloatCC::GreaterThanOrEqual` but should be correctly translated to `FloatCC::UnorderedOrGreaterThanOrEqual` and `FloatCC::UnorderedOrGreaterThan`. This change adds the necessary legalizations to make use of these new encodings.

cranelift/filetests/filetests/isa/x86/simd-comparison-run.clif

@@ -231,3 +231,17 @@ ebb0:
     return v8
 }
 ; run
+
+function %fcmp_gt_nans_f32x4() -> b1 {
+ebb0:
+    v0 = vconst.f32x4 [NaN 0x42.0 -NaN NaN]
+    v1 = vconst.f32x4 [NaN NaN 0x42.0 Inf]
+    v2 = fcmp gt v0, v1
+    ; now check that the result v2 is all zeroes
+    v3 = vconst.i32x4 0x00
+    v4 = raw_bitcast.i32x4 v2
+    v5 = icmp eq v3, v4
+    v8 = vall_true v5
+    return v8
+}
+; run