Unusable syscall numbers defined for riscv32gc-unknown-linux-gnu

[taiki-e]

riscv32gc-unknown-linux-gnu currently defines this:

libc/src/unix/linux_like/linux/gnu/b32/riscv32/mod.rs

Line 667 in 74e58cc

pub const SYS_futex: c_long = 98;

But riscv32 doesn't have time32 syscalls:
https://github.com/torvalds/linux/blob/v7.1/arch/riscv/kernel/Makefile.syscalls
https://github.com/torvalds/linux/blob/v7.1/include/uapi/asm-generic/unistd.h#L269
https://github.com/bminor/glibc/blob/glibc-2.42/sysdeps/unix/sysv/linux/riscv/rv32/arch-syscall.h#L64-L68

These must either be left undefined or aliased to time64 syscalls, as musl does:

libc/src/unix/linux_like/linux/musl/b32/riscv32/mod.rs

Line 647 in 74e58cc

pub const SYS_futex: c_long = SYS_futex_time64;

I only checked the SYS_futex, but other time32 system calls may have the same issue.

[tgross35]

Any chance you have a setup to run libc-test on that target? I expect there are probably a handful of things that aren't quite right about it since we don't test.

Happy to take a patch for it of course, in any case.