[Gradle, JS] Use disambiguation classifier in platform only for both

#KT-38635 fixed

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/KotlinJsTarget.kt

@@ -51,7 +51,11 @@ constructor(
         }
 
     val disambiguationClassifierInPlatform: String?
-        get() = disambiguationClassifier?.removeJsCompilerSuffix(KotlinJsCompilerType.LEGACY)
+        get() = if (irTarget != null) {
+            disambiguationClassifier?.removeJsCompilerSuffix(KotlinJsCompilerType.LEGACY)
+        } else {
+            disambiguationClassifier
+        }
 
     override val kotlinComponents: Set<KotlinTargetComponent> by lazy {
         if (irTarget == null)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/ir/KotlinJsIrTarget.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * 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.
  */
 
@@ -45,7 +45,11 @@ constructor(
         }
 
     val disambiguationClassifierInPlatform: String?
-        get() = disambiguationClassifier?.removeJsCompilerSuffix(KotlinJsCompilerType.IR)
+        get() = if (mixedMode) {
+            disambiguationClassifier?.removeJsCompilerSuffix(KotlinJsCompilerType.IR)
+        } else {
+            disambiguationClassifier
+        }
 
     override val binaries: KotlinJsBinaryContainer
         get() = compilations.withType(KotlinJsIrCompilation::class.java)