Improve handling of trailing declaration annotations.

Before:
void aaaaaaaaaaaa(int aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa) GUARDED_BY(
    aaaaaaaaaaaaa);

After:
void aaaaaaaaaaaa(int aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa)
    GUARDED_BY(aaaaaaaaaaaaa);

Also did some formatting cleanups with clang-format on the way.