Allow breaking after the trailing const after a function declaration.

Before:
void aaaaaaaaaaaa(int aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa) const GUARDED_BY(
    aaaaaaaaaaaaa);

After:
void aaaaaaaaaaaa(int aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa) const
    GUARDED_BY(aaaaaaaaaaaaa);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172718 91177308-0d34-0410-b5e6-96231b3b80d8