Changed some recently added //+ usages to #+ and also fixed some //+ usages in some code generators.

tests/core/sys/windows/win32gen/win32gen.cpp

@@ -902,7 +902,7 @@ static void verify_error_helpers(ofstream& out) {
 }
 
 static void test_core_sys_windows(ofstream& out) {
-	out << "//+build windows" << endl
+	out << "#+build windows" << endl
 		<< "package " << __func__
 		<< " // generated by " << path(__FILE__).filename().replace_extension("").string() << endl
 		<< endl