Correct PTHREAD_STACK_MIN for riscv64-linux-gnu

Author: andreas-schwab

src/unix/linux_like/linux/gnu/mod.rs

@@ -907,7 +907,8 @@ cfg_if! {
         target_arch = "arm",
         target_arch = "x86",
         target_arch = "x86_64",
-        target_arch = "s390x"
+        target_arch = "s390x",
+        target_arch = "riscv64"
     ))] {
         pub const PTHREAD_STACK_MIN: ::size_t = 16384;
     } else if #[cfg(any(