In builds without --enable-cassert (I guess not many developers use
those a lot), there are quite a few unused variable warnings. These
usually hold some intermediate result that the assert checks later. I
see that in some places our code already uses #ifdef
USE_ASSERT_CHECKING, presumably to hide similar issues. But in most
cases using this would significantly butcher the code. I found that
adding __attribute__((unused)) is cleaner. Attached is a patch that
cleans up all the warnings I encountered.
