make memcmp return a value of c_int_width instead of i32

compiler/rustc_codegen_llvm/src/common.rs

@@ -147,6 +147,10 @@ impl<'ll, 'tcx> ConstMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         self.const_uint(self.type_i1(), val as u64)
     }
 
+    fn const_i16(&self, i: i16) -> &'ll Value {
+        self.const_int(self.type_i16(), i as i64)
+    }
+
     fn const_i32(&self, i: i32) -> &'ll Value {
         self.const_int(self.type_i32(), i as i64)
     }