clang-format: Less eagerly try to keep label-value pairs on a line.

Before:
  string v =
      StrCat("aaaaaaaaaaaaaaaaaaaaaaaaaaa: ", SomeFunction(aaaaaaaaaaaa,
                                                           aaaaaaaaaaaaaaa),
             bbbbbbbbbbbbbbbbbbbbbbb);

After:
  string v = StrCat("aaaaaaaaaaaaaaaaaaaaaaaaaaa: ",
                    SomeFunction(aaaaaaaaaaaa, aaaaaaaaaaaaaaa),
                    bbbbbbbbbbbbbbbbbbbbbbb);

llvm-svn: 290337