I just took a look at the Squawk library on GitHub. For the Arduino Leonardo (or anything ATmega32U4 based), they recommend using Pin 5.
From the code for the Squawk_player.ino sketch on GitHub:
Pin 5 is currently used for the Right Arrow button. If we want to move the speaker to a PWM pin then we're already making the production version incompatible with the Dev Kit version. Therefore, moving the Right Arrow button to another pin, so pin 5 can be used for the speaker, should be acceptable.
Changes to the Arduboy library and/or existing sketches would be minor, but we would probably need separate Dev and production versions of them. They could use the same source files with just conditionally compiled sections based on a define
// Uncomment the following define for the Dev Kit version
#define RIGHT 6
#define SPEAKER 5
#define RIGHT 5
#define SPEAKER A2