Add runtime string concat options. Some renaming

compiler/config.jvm/src/org/jetbrains/kotlin/config/JVMConfigurationKeys.java

@@ -111,6 +111,9 @@ public class JVMConfigurationKeys {
     public static final CompilerConfigurationKey<Boolean> EMIT_JVM_TYPE_ANNOTATIONS =
             CompilerConfigurationKey.create("Emit JVM type annotations in bytecode");
 
+    public static final CompilerConfigurationKey<JvmRuntimeStringConcat> RUNTIME_STRING_CONCAT =
+            CompilerConfigurationKey.create("Specifies string concatenation scheme");
+
     public static final CompilerConfigurationKey<List<String>> KLIB_PATHS =
             CompilerConfigurationKey.create("Paths to .klib libraries");
 

compiler/config.jvm/src/org/jetbrains/kotlin/config/JvmRuntimeStringConcat.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.config
+
+enum class JvmRuntimeStringConcat {
+    DISABLE,
+    ENABLE, // makeConcatWithConstants
+    INDY; // makeConcat
+
+    val isDynamic
+        get() = this != DISABLE
+
+    companion object {
+        @JvmStatic
+        fun fromString(string: String) = values().find { it.name == string.toUpperCase() }
+    }
+}