Kernel+LibC+LibCore: Implement the unlinkat(2) syscall

Author: https://github.com/sin-ack
Commit: bc7c8879c5
Pull-request: https://github.com/SerenityOS/serenity/pull/13671
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/BertalanD
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/timschumi ✅

Userland/Libraries/LibC/unistd.cpp

@@ -644,7 +644,13 @@ int link(char const* old_path, char const* new_path)
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlink.html
 int unlink(char const* pathname)
 {
-    int rc = syscall(SC_unlink, pathname, strlen(pathname));
+    return unlinkat(AT_FDCWD, pathname, 0);
+}
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlinkat.html
+int unlinkat(int dirfd, char const* pathname, int flags)
+{
+    int rc = syscall(SC_unlink, dirfd, pathname, strlen(pathname), flags);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }