I was curious about the GCC port as I've spent far, far too much time looking through GCC support for various platforms and I have no memory of this target. Turns out it was an entirely independent effort, and probably a one-off:
https://groups.google.com/g/comp.sys.transputer/c/Zt6WNxneS08/m/ZBRytllF_X8J . The standard C compiler was a different beast, and I was not immediately able to recognize its lineage; it may have been developed from scratch.