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

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

Author: alistair23

library/std/src/sys_common/alloc.rs

@@ -14,7 +14,8 @@ use crate::ptr;
     target_arch = "powerpc64",
     target_arch = "asmjs",
     target_arch = "wasm32",
-    target_arch = "hexagon"
+    target_arch = "hexagon",
+    target_arch = "riscv32"
 )))]
 pub const MIN_ALIGN: usize = 8;
 #[cfg(all(any(