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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172200 91177308-0d34-0410-b5e6-96231b3b80d8