tools: acrn-crashlog: remove unsafe apis in usercrash

Since strlen/vsnprintf/ato* api are not safe, so use strnlen instead of
strlen, use vasprintf instead of vsnprintf and use strtol instead of
atoi.

Tracked-On: #1254
Signed-off-by: xiaojin2 <xiaojing.liu@intel.com>
Reviewed-by: Huang Yonghua <yonghua.huang@intel.com>
Reviewed-by: Liu, Xinwu <xinwu.liu@intel.com>
Acked-by: Chen Gang <gang.c.chen@intel.com>

tools/acrn-crashlog/usercrash/debugger.c

@@ -53,7 +53,7 @@ int main(int argc, char *argv[])
 
 	if (argc == 2) {
 		/* it's from shell cmd */
-		pid = atoi(argv[1]);
+		pid = (int)strtol(argv[1], NULL, 10);
 		crash_dump(pid, 0, STDOUT_FILENO);
 	} else {
 		print_usage();