Apply clang-format universally.

* It is tough to contribute to a project that doesn't use a formatter,
* It is extra hard to contribute to a project which has configured the formatter, but ignores it for some files
* Code formatting makes it harder to hide obscure / weird bugs by accident or on purpose,

Let's rip the bandaid off?

Note that PRs currently in flight should be able to be merged relatively easily by applying `clang-format` to their tip prior to merge.

src/libexpr/function-trace.cc

@@ -19,4 +19,4 @@ void FunctionCallTrace::postFunctionCallHook(
     printMsg(lvlInfo, "function-trace exited %1% at %2%", state.positions[pos], ns.count());
 }
 
-}
+} // namespace nix