Add more tests for RGBASM code coverage (#1257)

* Add more tests for RGBASM code coverage

* Use C++ unnamed parameters, not `(void)` casting

* Fix crash in `sect_AlignPC` from #1253

src/link/main.cpp

@@ -406,7 +406,6 @@ int main(int argc, char *argv[])
 			break;
 		case 's':
 			// TODO: implement "smart linking" with `-s`
-			(void)musl_optarg;
 			warning(NULL, 0, "Nobody has any idea what `-s` does");
 			break;
 		case 't':