Support synthetic flag

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/FunctionCodegen.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.backend.jvm.codegen
 
 import org.jetbrains.kotlin.backend.common.lower.DECLARATION_ORIGIN_FUNCTION_FOR_DEFAULT_PARAMETER
+import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
 import org.jetbrains.kotlin.backend.jvm.descriptors.JvmDescriptorWithExtraFlags
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns.FQ_NAMES
 import org.jetbrains.kotlin.codegen.*
@@ -91,7 +92,7 @@ open class FunctionCodegen(private val irFunction: IrFunction, private val class
             else -> if (classCodegen.irClass.isJvmInterface && irFunction.body == null) Opcodes.ACC_ABSTRACT else 0 //TODO transform interface modality on lowering to DefaultImpls
         }
         val nativeFlag = if (irFunction.isExternal) Opcodes.ACC_NATIVE else 0
-
+        val syntheticFlag = if (irFunction.origin == JvmLoweredDeclarationOrigin.SYNTHETIC_ACCESSOR) Opcodes.ACC_SYNTHETIC else 0
         return visibility or
                 modalityFlag or
                 staticFlag or
@@ -99,6 +100,7 @@ open class FunctionCodegen(private val irFunction: IrFunction, private val class
                 deprecation or
                 nativeFlag or
                 bridgeFlag or
+                syntheticFlag or
                 (if (descriptor is JvmDescriptorWithExtraFlags) descriptor.extraFlags else 0)
     }