revlog: give formatting to clang-format This has two lines that are poorly formatted, both right after PyObject_HEAD macros. It's possible that in the future there will be a feature to tell clang-format that a token includes an end-of-line character (in this case the ;), but for now I'm willing to live with two poorly-formatted lines in a struct definition in exchange for not thinking about how this file is formatted. Differential Revision: https://phab.mercurial-scm.org/D5234