Allow breaking after the return type in function declarations.

This has so far been disabled for Google style, but should be done
before breaking at nested name specifiers or in template parameters.

Before (in Google style):
template <typename T>
aaaaaaaa::aaaaa::aaaaaa<T, aaaaaaaaaaaaaaaaaaaaaaaaa> aaaaaaaaaaaaaaaaaaaaaaaa<
    T>::aaaaaaa() {}

After:
template <typename T>
aaaaaaaa::aaaaa::aaaaaa<T, aaaaaaaaaaaaaaaaaaaaaaaaa>
aaaaaaaaaaaaaaaaaaaaaaaa<T>::aaaaaaa() {}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175074 91177308-0d34-0410-b5e6-96231b3b80d8