alignof is an operator in C23.

--- CSSC-1.4.1/gl/tests/test-stdalign.c	2016-02-07 11:24:40.000000000 +0000
+++ CSSC-1.4.1/gl/tests/test-stdalign.c	2025-07-05 02:56:01.611062240 +0100
@@ -33,11 +33,6 @@
 typedef struct { char a[3]; } struct3;
 typedef struct { char a[4]; } struct4;
 
-verify (__alignof_is_defined == 1);
-#ifndef alignof
-# error "alignof is not a macro"
-#endif
-
 #if __alignas_is_defined
 verify (__alignas_is_defined == 1);
 # ifndef alignas