Fix Wall errors in the codebase

[DizzyEggg]

Fixes all(or part) of the currently occurring errors in our codebase. This is the next step after #3165 in our quest to ditch agbcc.

Some notes:

• Turns out there were a couple of actual errors/UBs in our code(i.e. see IncreaseStatUpScore changes). They are fixed now.
• Unused GF's function use the unused attribute now. Dummies/dumb functions are removed. Unused functions written by us are commented out.
• I had to, and probably will have to still do, do some ugly casts/memcpy calls to get around strict aliasing and signedness
• There were lots of non-void functions without a return statement and unused or just set variables in functions.

[DizzyEggg]

This is, in theory, complete. I might have made some questionable decisions with how I handled some compiler errors, so I'm open to discussion.
Things like changing s16 to u16 or u16 to s16 should be tested as things may break there. They already did for me once with the door animations(fixed now.)

[DizzyEggg]

au revoir 3267