Legalize brz.i128 and brnz.i128

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

@@ -0,0 +1,24 @@
+test compile
+target x86_64
+
+function u0:0(i128) -> i8 fast {
+ebb0(v0: i128):
+    brz v0, ebb1
+    v1 = iconst.i8 0
+    return v1
+
+ebb1:
+    v2 = iconst.i8 1
+    return v2
+}
+
+function u0:1(i128) -> i8 fast {
+ebb0(v0: i128):
+    brnz v0, ebb1
+    v1 = iconst.i8 0
+    return v1
+
+ebb1:
+    v2 = iconst.i8 1
+    return v2
+}