Revert "Remove obsolete kotlin.build.useIR flag"

This reverts commit 91e47f1fd7.

kotlin-native/build.gradle

@@ -120,6 +120,15 @@ allprojects {
         }
     }
 
+    if (findProperty("kotlin.build.useIR") == "true") {
+        tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
+            kotlinOptions {
+                useIR = true
+                freeCompilerArgs += ["-Xir-binary-with-stable-abi"]
+            }
+        }
+    }
+
     setupHostAndTarget()
     loadCommandLineProperties()
     loadLocalProperties()

kotlin-native/gradle.properties

@@ -34,4 +34,6 @@ ktorVersion=1.2.1
 shadowVersion=5.1.0
 metadataVersion=0.0.1-dev-10
 
-kotlinNativeVersionInResources=true
+# Uncomment to compile Kotlin/Native backend modules with JVM IR backend.
+# kotlin.build.useIR=true
+kotlinNativeVersionInResources=true