The documentation for libgccjit is now visible on the GCC website in HTML form at: https://gcc.gnu.org/onlinedocs/jit/ (and is being built nightly).
Thanks to everyone who helped make this happen (Gerald Pfeifer, Joseph Myers, Frank Ch. Eigler, Jeff Law, iirc). The "Show Source" links on each page are currently 404s, but that should be resolved shortly. Dave