Change clang-format's affinity for breaking after return types.

Change clang-format's affinity for breaking after return types.

Function declarations are now broken with the following preferences:
1) break amongst arguments.
2) break after return type.
3) break after (.
4) break before after nested name specifiers.

Options #2 or #3 are preferred over #1 only if a substantial number of
lines can be saved by that.

llvm-svn: 179287