Update to origin/master.

IrReturn should return 'Unit' for "return without value".

compiler/testData/ir/irText/expressions/smartCasts.txt

@@ -18,6 +18,7 @@ FILE /smartCasts.kt
           if: TYPE_OP origin=NOT_INSTANCEOF typeOperand=kotlin.String
             GET_VAR 'value-parameter x: Any' type=kotlin.Any origin=null
           then: RETURN type=kotlin.Nothing from='test1(Any): Unit'
+            GET_OBJECT 'Unit' type=kotlin.Unit
       CALL 'println(Int): Unit' type=kotlin.Unit origin=null
         message: CALL '<get-length>(): Int' type=kotlin.Int origin=GET_PROPERTY
           $this: TYPE_OP origin=IMPLICIT_CAST typeOperand=kotlin.String

compiler/testData/ir/irText/expressions/smartCastsWithDestructuring.txt

@@ -16,6 +16,7 @@ FILE /smartCastsWithDestructuring.kt
           if: TYPE_OP origin=NOT_INSTANCEOF typeOperand=I2
             GET_VAR 'value-parameter x: I1' type=I1 origin=null
           then: RETURN type=kotlin.Nothing from='test(I1): Unit'
+            GET_OBJECT 'Unit' type=kotlin.Unit
       COMPOSITE type=kotlin.Unit origin=DESTRUCTURING_DECLARATION
         VAR IR_TEMPORARY_VARIABLE val tmp0_container: I1
           GET_VAR 'value-parameter x: I1' type=I1 origin=null

compiler/testData/ir/irText/expressions/tryCatchWithImplicitCast.txt

@@ -6,6 +6,7 @@ FILE /tryCatchWithImplicitCast.kt
           if: TYPE_OP origin=NOT_INSTANCEOF typeOperand=kotlin.String
             GET_VAR 'value-parameter a: Any' type=kotlin.Any origin=null
           then: RETURN type=kotlin.Nothing from='testImplicitCast(Any): Unit'
+            GET_OBJECT 'Unit' type=kotlin.Unit
       VAR val t: kotlin.String
         TRY type=kotlin.String
           try: BLOCK type=kotlin.String origin=null