linux-user: Implement starttime field in self stat emulation

Instead of always returning 0, return actual starttime.

Signed-off-by: Cameron Esfahani <dirty@apple.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220128001251.45165-1-dirty@apple.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 9d2b311..98dfbf2 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -154,6 +154,9 @@
 
     /* This thread's sigaltstack, if it has one */
     struct target_sigaltstack sigaltstack_used;
+
+    /* Start time of task after system boot in clock ticks */
+    uint64_t start_boottime;
 } TaskState;
 
 abi_long do_brk(abi_ulong new_brk);