[RFC PATCH 09/12] riscv: Add support for kernel-mode FPU

[Christoph Hellwig]

> +#ifdef __riscv_f
> +
> +#define kernel_fpu_begin() \
> +	static_assert(false, "floating-point code must use a separate translation unit")
> +#define kernel_fpu_end() kernel_fpu_begin()
> +
> +#else
> +
> +void kernel_fpu_begin(void);
> +void kernel_fpu_end(void);
> +
> +#endif

I'll assume this is related to trick that places code in a separate
translation unit, but I fail to understand it.  Can you add a comment
explaining it?