Fix file descriptor unlimited growth.

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/library/CombinedIrFileAccessor.kt

@@ -31,7 +31,9 @@ fun File.map(mode: FileChannel.MapMode = FileChannel.MapMode.READ_ONLY,
         if (mode == FileChannel.MapMode.READ_ONLY) "r" else "rw")
     val fileSize = if (mode == FileChannel.MapMode.READ_ONLY)
         file.length() else size.also { assert(size != -1L) }
-    return file.channel.map(mode, start, fileSize) // Shall we .also { file.close() }?
+    val channel = file.channel
+    return channel.map(mode, start, fileSize)
+        .also { channel.close() } // Channel close closes the file also.
 }
 
 class CombinedIrFileReader(file: File) {