Agreed Dave Conroy is the real hero here. In 1975 I worked for Teklogix in Canada where Dave had worked and was still doing some consulting. He'd just finished University of Waterloo and wrote a C compiler for RSX11M.
Vik Sondi and I were the first two people I know of to use it, presumably others at Waterlook did, although I went there the next year and met most of the Unix poeple and never saw Dave's compiler used there - we didn't need to we had real Bell Labs Unix on a PDP 11/45 and it *had* a C compiler already - they had no need of RSX there. And we sure coldn't use Unix for real work. And RT-11 Sucked. Badly.
Dave gave the compiler to DECUS, the DEC users group. It popped up on my radar in Los Angeles in 1984 when we used it to generate Z8000 code. I noticed Dave's name was still in it. By 1992 or so I'd noticed the free C compiler I got from John "hoptoad" Gilmore's site said it was a port of the DECUS C compiler - and was now called "gcc".
I dunno what RMS wrote, but from what I've seen Dave Conroy wrote what is now called gcc.
As an aside, I met Charles Forsyth briefly at Waterloo. He looked a bit like a grown up Harry Potter and always wore a blue blazer. Dave looked like a deadhead, they were quite the pair.