FIR: Fix main fn mangling (without proper detection)

proper main function detector has to be implemented in addition
to that

compiler/fir/fir2ir/jvm-backend/src/org/jetbrains/kotlin/fir/backend/jvm/FirJvmMangleComputer.kt

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.backend.common.serialization.mangle.MangleMode
 import org.jetbrains.kotlin.backend.common.serialization.mangle.collectForMangler
 import org.jetbrains.kotlin.fir.*
 import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.resolve.firProvider
 import org.jetbrains.kotlin.fir.resolve.symbolProvider
 import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
 import org.jetbrains.kotlin.fir.resolve.toSymbol
@@ -35,6 +36,11 @@ open class FirJvmMangleComputer(
 
     open fun FirFunction<*>.platformSpecificFunctionName(): String? = null
 
+    open fun FirFunction<*>.platformSpecificSuffix(): String? =
+        if (this is FirSimpleFunction && name.asString() == "main")
+            this@FirJvmMangleComputer.session.firProvider.getFirCallableContainerFile(symbol)?.name
+        else null
+
     open fun FirFunction<*>.specialValueParamPrefix(param: FirValueParameter): String = ""
 
     private fun addReturnType(): Boolean = false
@@ -121,6 +127,11 @@ open class FirJvmMangleComputer(
         val name = (this as? FirSimpleFunction)?.name ?: Name.special("<anonymous>")
         builder.append(name.asString())
 
+        platformSpecificSuffix()?.let {
+            builder.append(MangleConstant.PLATFORM_FUNCTION_MARKER)
+            builder.append(it)
+        }
+
         mangleSignature(isCtor, isStatic)
     }
 

compiler/testData/codegen/box/package/mainInFiles.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // TARGET_BACKEND: JVM
 
 // WITH_RUNTIME