So... where is it?
RMS's link: https://savannah.gnu.org/git/?group=c-intro-and-ref
click "browse sources repository" https://git.savannah.nongnu.org/cgit/c-intro-and-ref.git
hunt for the word "tree" and click it: https://git.savannah.nongnu.org/cgit/c-intro-and-ref.git/tre...
Oh look, a directory listing! Click the manual! https://git.savannah.nongnu.org/cgit/c-intro-and-ref.git/tre...
What, you don't want to read the 13k-line tex source? Sorry. Clone it and build it yourself, I guess.
They don't try to hide them. This is the git repo of the new version of the C reference and will end up on that page at some point, replacing the one there now.
git clone https://git.savannah.gnu.org/git/c-intro-and-ref.gitIt's in the Texinfo format though, so you'd probably want to texi2html it.
Or just
make c.html