io: remove unused Zzz_CoerceInterfaceTableGeneration struct; add test for `x := Enum{}`

vlib/io/readerwriter.v

@@ -31,19 +31,3 @@ pub fn make_readerwriter(r Reader, w Writer) ReaderWriterImpl {
 		w: w
 	}
 }
-
-struct Zzz_CoerceInterfaceTableGeneration {
-}
-
-fn (_ Zzz_CoerceInterfaceTableGeneration) write(buf []byte) ?int {
-	return none
-}
-
-fn (_ Zzz_CoerceInterfaceTableGeneration) read(mut buf []byte) ?int {
-	return none
-}
-
-fn zzz_reader_writer_coerce_compiler() {
-	x := Zzz_CoerceInterfaceTableGeneration{}
-	_ := make_readerwriter(x, x)
-}

vlib/v/gen/c/cgen.v

@@ -5037,11 +5037,9 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 		g.indent--
 	}
 
-	if g.pref.ccompiler == 'msvc' {
 	if !initialized {
 		g.write('\n#ifndef __cplusplus\n0\n#endif\n')
 	}
-	}
 
 	g.write('}')
 	if g.is_shared && !g.inside_opt_data && !g.is_array_set {

vlib/v/tests/enum_test.v

@@ -118,3 +118,18 @@ fn test_typed_enum() {
 	}
 }
 */
+
+enum FileType {
+	unknown
+	wiki
+	file
+	image
+	html
+}
+
+fn test_enum_instance() {
+	mut filetype := FileType{}
+	eprintln(filetype)
+	s := 'x $filetype z'
+	assert s == 'x unknown z'
+}