This is one of the clearest clues that these hyphenated words are Tolkien’s putative translation artifacts. If I were decsribing this scene about a person of my own species, I would say that the steps were not made, all the same, for a child’s legs, or for a middle-aged woman’s legs…
[13.044] The steps were not made, all the same, for hobbit-legs, and Bilbo was just feeling that he could go on no longer, when suddenly the roof sprang high and far beyond the reach of their torch-light.
I believe that “hobbit-legs” indicates a single word like “shank”, in Westron, meant to convey “the legs of a hobbit” – a very specialized word indeed. The passage takes place as Bilbo and the dwarves clamber through the Mountain to the chamber of Thror.
Although “Hobbit” is listed in OED – and an invention of Tolkien’s – no hyphenated forms are.
“hobbit, n.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/87449. Accessed 14 September 2017.