Add test

cranelift/filetests/filetests/isa/x86/i128.clif

@@ -0,0 +1,13 @@
+test compile
+target x86_64
+
+function u0:0(i128) -> i128 fast {
+ebb0(v0: i128):
+    v1 = iconst.i64 0
+    v2 = iconst.i64 42
+    v3 = iconcat.i64 v1, v2
+    return v3
+    ; check: v1 = iconst.i64 0
+    ; check: v2 = iconst.i64 42
+    ; check: return v1, v2, v7
+}