Fix function-exists() to also handle built-in functions
Fix function-exists() to also handle built-in functions

g105b/scssphp,webdevid/scssphp,dleffler/scssphp,dleffler/scssphp,webdevid/scssphp,dleffler/scssphp,leafo/scssphp,leafo/scssphp,g105b/scssphp,leafo/scssphp,webdevid/scssphp,g105b/scssphp,kkkyyy03/scssphp