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/syscall.c b/linux-user/syscall.c
index 84cfa22..b3948d1 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8077,6 +8077,9 @@
         } else if (i == 3) {
             /* ppid */
             g_string_printf(buf, FMT_pid " ", getppid());
+        } else if (i == 21) {
+            /* starttime */
+            g_string_printf(buf, "%" PRIu64 " ", ts->start_boottime);
         } else if (i == 27) {
             /* stack bottom */
             g_string_printf(buf, TARGET_ABI_FMT_ld " ", ts->info->start_stack);