v.gen.c: add coutput tests for the [console] codegen to prevent future regressions

vlib/v/gen/c/fn.v

@@ -1483,7 +1483,7 @@ fn (mut g Gen) ref_or_deref_arg(arg ast.CallArg, expected_type ast.Type, lang as
 }
 
 fn (mut g Gen) is_gui_app() bool {
-	$if windows {
+	if g.pref.os == .windows {
 		if g.force_main_console {
 			return false
 		}

vlib/v/gen/c/testdata/console_windows_program.c.must_have

@@ -0,0 +1 @@
+int wmain(int ___argc, wchar_t* ___argv[], wchar_t* ___envp[]){

vlib/v/gen/c/testdata/console_windows_program.vv

@@ -0,0 +1,6 @@
+// vtest vflags: -cc msvc -os windows
+
+[console]
+fn main() {
+	println('hello world')
+}

vlib/v/gen/c/testdata/gui_windows_program.c.must_have

@@ -0,0 +1 @@
+int WINAPI wWinMain(HINSTANCE instance, HINSTANCE prev_instance, LPWSTR cmd_line, int show_cmd){

vlib/v/gen/c/testdata/gui_windows_program.vv

@@ -0,0 +1,8 @@
+// vtest vflags: -cc msvc -os windows
+import sokol
+
+const used_import = sokol.used_import
+
+fn main() {
+	println('hello world')
+}

vlib/v/gen/c/testdata/gui_windows_program_with_console_tag.c.must_have

@@ -0,0 +1 @@
+int wmain(int ___argc, wchar_t* ___argv[], wchar_t* ___envp[]){

vlib/v/gen/c/testdata/gui_windows_program_with_console_tag.vv

@@ -0,0 +1,9 @@
+// vtest vflags: -cc msvc -os windows
+import sokol
+
+const used_import = sokol.used_import
+
+[console]
+fn main() {
+	println('hello world')
+}