CODEGEN: don't generate getters/setters and other functions with descriptor.modality == Modality.ABSTRACT

(cherry picked from commit 0ca5bc071f64a5eb68f49896c8b5b28952ec6126)

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/IrToBitcode.kt

@@ -222,6 +222,8 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
 
     override fun visitFunction(declaration: IrFunction) {
         logger.log("visitFunction                  : ${ir2string(declaration)}")
+        if (declaration.descriptor.modality == Modality.ABSTRACT)
+            return
         codegen.function(declaration)
         metadator.function(declaration)
         declaration.acceptChildrenVoid(this)