Include function to find symbol on the symbols table

Signed-off-by: Gustavo Toshi Komura <gtk10@c3sl.ufpr.br>
Check in the atribuition if the symbol was declared

Signed-off-by: Gustavo Toshi Komura <gtk10@c3sl.ufpr.br>
Update test to check if the symbols was declared

Signed-off-by: Gustavo Toshi Komura <gtk10@c3sl.ufpr.br>
Execute make

Signed-off-by: Gustavo Toshi Komura <gtk10@c3sl.ufpr.br>