library/std: linux: Add support for RISC-V 32-bit

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

Author: alistair23

library/std/src/os/linux/raw.rs

@@ -234,7 +234,8 @@ mod arch {
     target_arch = "mips64",
     target_arch = "s390x",
     target_arch = "sparc64",
-    target_arch = "riscv64"
+    target_arch = "riscv64",
+    target_arch = "riscv32"
 ))]
 mod arch {
     pub use libc::{blkcnt_t, blksize_t, ino_t, nlink_t, off_t, stat, time_t};