Fix 28 gcc output parse error

Fix #28:

1. Modified gcc output parser to output an error for the case mentioned in the issue.
2. Updated/fixed the linker test in the parser spec.
3. Just as a fallback, if the compilation fails but the parser fails to return any errors, the error label shows a generic message instead of the error/warning count. Previously, the error label was empty, so the user couldn't click on it to reveal the gcc output window.
4. `index.html` cleanup