Fix compiler errors under clang.

[edre]

Don't end a block with a label, and add a block around labels that define variables.

[richardjs]

Thanks! There's likely a number of C irregularities around the code (I only use C for game AIs), so feel free to point out or correct anything you see.

[edre]

My day job is C++, so I use the same strategy for C: blindly do what the compiler tells me ;)