you cannot, as linux code is using a lot of gcc/clang extensions stuff, namely this is some sort of C dialect, not really C. Almost at every new release of linux, "somebody" did manage to commit into its code the usage of new gcc/clang extensions.

The right(TM) way would be to port linux to simple and lean C (like some simple C89 with benign bits of c99/c11): the price is some loss of performance which could be partially mitigated with an assembly port of critical fast-paths (I guess that would show on really loaded servers only).

In the end, if RISC-V is a success, namely a world with a pertinent ISA without toxic IP tied to it (like x86/arm), then a full assembly port of linux would be more than interesting in order to rid it from compiler tantrums.