Check named-args-for-clarity incur no extra bytecode

When named arguments correspond the the parameter declaration
order, the compiler should not lift out assignments before
the method call, as it would have to do for out-of-order
arguments.

Confirm this with a bytecode comparison test.

Author: retronym

test/files/jvm/named-args-in-order.check

@@ -0,0 +1,3 @@
+bytecode identical
+bytecode identical
+bytecode identical

test/files/jvm/named-args-in-order/SameBytecode.scala

@@ -0,0 +1,9 @@
+class SameBytecode {
+  def foo(a: Int, b: String) = 0
+  def foo(a: Int, b: Any) = 0
+
+  def a = foo(0, "")
+  def b = foo(a = 0, "")
+  def c = foo(0, b = "")
+  def d = foo(a = 0, b = "")
+}

test/files/jvm/named-args-in-order/Test.scala

@@ -0,0 +1,10 @@
+import scala.tools.partest.BytecodeTest
+
+object Test extends BytecodeTest {
+  def show: Unit = {
+    val classNode = loadClassNode("SameBytecode")
+    def sameAsA(meth: String) =
+      sameBytecode(getMethod(classNode, "a"), getMethod(classNode, meth))
+    Seq("b", "c", "d").foreach(sameAsA)
+  }
+}