Add chown() syscall and a simple /bin/chown program.

Userland/chown.cpp

@@ -0,0 +1,43 @@
+#include <unistd.h>
+#include <sys/stat.h>
+#include <stdio.h>
+#include <string.h>
+#include <AK/AKString.h>
+
+int main(int argc, char **argv)
+{
+    if (argc < 2) {
+        printf("usage: chown <uid[:gid]> <path>\n");
+        return 0;
+    }
+
+    uid_t new_uid = -1;
+    gid_t new_gid = -1;
+
+    auto parts = String(argv[1]).split(':');
+    if (parts.is_empty()) {
+        fprintf(stderr, "Empty uid/gid spec\n");
+        return 1;
+    }
+    bool ok;
+    new_uid = parts[0].to_uint(ok);
+    if (!ok) {
+        fprintf(stderr, "Invalid uid: '%s'\n", parts[0].characters());
+        return 1;
+    }
+    if (parts.size() == 2) {
+        new_gid = parts[1].to_uint(ok);
+        if (!ok) {
+            fprintf(stderr, "Invalid gid: '%s'\n", parts[1].characters());
+            return 1;
+        }
+    }
+
+    int rc = chown(argv[2], new_uid, new_gid);
+    if (rc < 0) {
+        perror("chown");
+        return 1;
+    }
+
+    return 0;
+}