From: Dan Gohman <dev@sunfishcode.online>
Subject: [PATCH] Define `TARGET_STAT_HAVE_NSEC` for s390x

Without this, The `fstat` syscall sets `st_mtime_nsec` and the other `_nsec`
fields to 0. Libc `fstat` will sometimes use the `fstatat` or `fstat64`
syscalls instead, which aren't affected, but the libc `fstat` on ubuntu-20.04
on Github Actions appears to be affected.

This can be seen in the `st_mtime_nsec` assert in tests/fs/futimens.rs.

It's not yet known why upstream qemu doesn't define this.

---
 linux-user/generic/sockbits.h | 1 +
 1 files changed, 1 insertions(+)

diff -ur a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h
--- a/linux-user/syscall_defs.h	2021-08-24 10:35:41.000000000 -0700
+++ b/linux-user/syscall_defs.h	2022-04-12 13:23:25.291064887 -0700
@@ -2040,6 +2040,7 @@
 	abi_long	__unused[3];
 };
 #elif defined(TARGET_S390X)
+#define TARGET_STAT_HAVE_NSEC
 struct target_stat {
     abi_ulong  st_dev;
     abi_ulong  st_ino;