The GLU library is built atop deprecated OpenGL functions, and needs to be purged from Blender's drawing code.
We must complete this task before switching to core profile.
grep -r glu[A-Z] source/blender to find the parts that need to be updated.
We should reimplement gluUnProject, but not the general shape & geometry evaluation library GLU provides. Visit each GLU-using function and determine the best way to perform its task.
grease pencil volumetric strokes & dots <-- major recode