The functions glutBitmapString and glutStrokeString are documented as taking arguments
void *font, char *string
But in freeglut_ext.h they are declared as taking the arguments
void* font, const unsigned char *string
I'm using Debian Sid and freeglut3-dev_2.4.0-6.1. Maybe the documentation is just out of date, because it says v2.0.0:
The same thing is in the documentation that accompanied freeglut3-dev in Debian.