Michel Gien lead a Unix reimplementation in Pascal (French SOL project) in the late 1970s/early 1980. Later they did a second version in C++ which was called Chorus. You'll have to ask Michel but I don’t think Sol required a C subsystem but I believe it had one to allow code to be imported.
I never knew what compiler his team used but I was once told it was the Amsterdam compilers. If that is true, you could claim there is the boot strap issue if you want to get into the purity of did it need C.
But once running there would not have been any need for it to be required. Plus, there were many Pascal compilers in Pascal in those days, but most of the compiler suites that allowed multiple front end were in C (such as the Amsterdam kit and gcc).
Sent from a handheld expect more typos than usual