Create a table with an integer primary key.
Create a second table with a foreign key on a bigint column that references to the integer primary key.
Using InnoDB storage engine.
Same as in 2007 - You will get error 150.
I am 120% sure that I already submitted a bug report in 2007 at MySQL. I am also almost sure that the old bug still is open but I couldn't find it.
Anyway, I attached a screen shot.
After Hartmut asked me if this works in PostgreSQL I tested and figured out foreign key bigint references to int works fine.