Just so you know, the folks in Western Electric's Teletype team retargeted the Ritchie compiler to become a Z80 cross-compiler/assembler dev tools suite. That implementation was floating around the Bell System in the 76/77/78 time frame. I know Karn had brought it with him and started using it for his original KA9Q IP/TCP implementation, initially for his CP/M box and ham radio system; (as he ran it as a cross compiler on my 11/34 at CMU's Mellon Institute -- I trade cycles for access to the compiler). I don't know if anyone ever tried to use the Teletype Z80 C compiler to build a UNIX or UNIX-like port for the z80 with it. I have since forgotten how complete it was.
A bit later, Loer Zohlman wrote BDS C, which was pretty darned good/fairly complete C implementation for the time; and a few years back, he put it in the Public Domain [ you can download it from his website]. Missing/lost is/was the UNIX-like system they were working on to go along with the compiler - which I am trying to remember if it was quite complete/much less made it out for sale like his compiler was at the time. However, at an early Boston USENIX, Leor had it running "good enough" that he brought it and showed it in his room on a dual floppy Z80 IMSAI box with some 4K bank switching HW (I don't remember how much memory - probably 128Kish). I was there when he demo'ed it to Dennis and a few other hackers. Dennis's response at the time was it reminded him of the early UNIX efforts. I just thought it was pretty cool.
A year or so later, Onyx folks brought their Z8000 based V7 system to USENIX, causing quite a stir
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