Add x86 unpack instructions

cranelift/filetests/filetests/isa/x86/simd-lane-access-binemit.clif

@@ -95,3 +95,17 @@ block0:
 [-, %xmm0]  v4 = x86_pshufb v1, v3           ; bin: 66 41 0f 38 00 c4
             return
 }
+
+;; pack/unpack
+
+function %unpack_high_i8x16(i8x16, i8x16) {
+block0(v0: i8x16 [%xmm0], v1: i8x16 [%xmm12]):
+[-, %xmm0]  v2 = x86_punpckh v0, v1         ; bin: 66 41 0f 68 c4
+            return
+}
+
+function %unpack_low_i32x4(i32x4, i32x4) {
+block0(v0: i32x4 [%xmm7], v1: i32x4 [%xmm6]):
+[-, %xmm7]  v2 = x86_punpckl v0, v1         ; bin: 66 0f 62 fe
+            return
+}

cranelift/filetests/filetests/isa/x86/simd-lane-access-run.clif

@@ -192,3 +192,16 @@ block0:
     return v5
 }
 ; run
+
+function %unpack_low() -> b1 {
+block0:
+    v0 = vconst.i32x4 [0 1 2 3]
+    v1 = vconst.i32x4 [4 5 6 7]
+    v2 = x86_punpckl v0, v1
+
+    v3 = vconst.i32x4 [0 4 1 5]
+    v4 = icmp eq v2, v3
+    v5 = vall_true v4
+    return v5
+}
+; run