Add Physical mode to realpath

This adds the 'Physical Mode' and 'Logical Mode' switches to realpath, which control when symlinks are resolved.

tests/by-util/test_realpath.rs

@@ -106,3 +106,36 @@ fn test_realpath_file_and_links_strip_zero() {
         .succeeds()
         .stdout_contains("bar\u{0}");
 }
+
+#[test]
+fn test_realpath_physical_mode() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+
+    at.mkdir("dir1");
+    at.mkdir_all("dir2/bar");
+    at.symlink_dir("dir2/bar", "dir1/foo");
+
+    scene
+        .ucmd()
+        .arg("dir1/foo/..")
+        .succeeds()
+        .stdout_contains("dir2\n");
+}
+
+#[test]
+fn test_realpath_logical_mode() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+
+    at.mkdir("dir1");
+    at.mkdir("dir2");
+    at.symlink_dir("dir2", "dir1/foo");
+
+    scene
+        .ucmd()
+        .arg("-L")
+        .arg("dir1/foo/..")
+        .succeeds()
+        .stdout_contains("dir1\n");
+}