Also in (3), very portable to old architectures. PCC is written in C, where LLVM/Clang is C++. This makes one less hurdle to bootstrapping a new compiler on some archs.
From experience in porting an OS, common porting scaffolding can include a cross compiler and a cross linker, and replacing an assembler with a compiler for compiling the assembly code for the new target box.
Getting a native build and a native C++ and a native assembler re-hosted can then proceed secondary to getting the basic OS pieces booted and rolling.
Getting a native build and a native C++ and a native assembler re-hosted can then proceed secondary to getting the basic OS pieces booted and rolling.