id: The --real flag should only affect -u, -g, and -G (#7796)

* id: The `--real` flag should only affect `-u`, `-g`, and `-U`

* id: Test output with different UID and EUID

* id: Simplify testing different UID and EUID

* id: Compile preload file for test using cc instead of gcc

* id: Remove test for different UID and EUID

The test is incompatible with some CI/CD targets.

This reverts the following commits:
- 8efcbf9ada
- 208fa8e7f8
- a498a2722d

src/uu/id/src/id.rs

@@ -238,10 +238,14 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
             return Ok(());
         }
 
-        let (uid, gid) = possible_pw.as_ref().map(|p| (p.uid, p.gid)).unwrap_or((
+        let (uid, gid) = possible_pw.as_ref().map(|p| (p.uid, p.gid)).unwrap_or({
-            if state.rflag { getuid() } else { geteuid() },
+            let use_effective = !state.rflag && (state.uflag || state.gflag || state.gsflag);
-            if state.rflag { getgid() } else { getegid() },
+            if use_effective {
-        ));
+                (geteuid(), getegid())
+            } else {
+                (getuid(), getgid())
+            }
+        });
         state.ids = Some(Ids {
             uid,
             gid,