From posix spec, if set-user-ID bit is set in the file permissions,
then the effective user ID of the new process shall be set to the
user ID of the new process image file.
Let's ignore whether ST_NOSUID is set on the mounted file system.
https://pubs.opengroup.org/onlinepubs/007904875/functions/exec.html
test step:
hello example build as a module and call geteuid and getegid API.
then set file binary set-user-ID bit on the host.
$ chmod +s apps/bin/hello
nsh> mount -t hostfs -o fs=. /data
nsh> ls -l /data/apps/bin/hello
-rwsrwsr-x 1000 1000 9264 /data/apps/bin/hello
nsh> /data/apps/bin/hello
geteuid:1000
getegid:1000
Signed-off-by: fangxinyong <fangxinyong@xiaomi.com>
2d73e86b47