[PATCH] riscv: Use __has_include__ to include <asm/syscalls.h> [BZ #24022]

[Florian Weimer]

* H. J. Lu:

> +#if __has_include__ (<asm/syscalls.h>)

Isn't __has_include (no trailing __) the more canonical name?
I think that's what's in C++17.