There's a lot of code in the file that is questionable to say the least. There are unnecessary blocks ( { ... }; ) of code with unnecessary semicolons that don't serve any logical purpose.

My hunch tells me it may be the result of macro-expansion in C (cc -E ...), etc. So it's likely there's a larger code base with multiple files and they expanded it into a one large C file (sometimes called an amalgamation build) and called it a day.

By they, I mean the OP, a script or an AI (or all three).