Support indy concatenation

compiler/testData/codegen/java9/box/concatDynamic.kt

@@ -0,0 +1,14 @@
+// KOTLIN_CONFIGURATION_FLAGS: RUNTIME_STRING_CONCAT=enable
+// JVM_TARGET: 9
+fun box(): String {
+    val p = 3147483648u
+    val a = "_"
+    val b = "_"
+    val s =  a + "1" + "2" + 3 + 4L + b + 5.0 + 6F + '7' + true + false + 3147483647u + p
+
+    return if (s != "_1234_5.06.07truefalse31474836473147483648") "fail $s" else "OK"
+}
+
+fun main() {
+    box().let { if (it != "OK") throw AssertionError(it) }
+}