Improve formatting of trailing annotations.

Before:
bool aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa __attribute__((
    unused));

After:
bool aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    __attribute__((unused));

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177034 91177308-0d34-0410-b5e6-96231b3b80d8