Variably modified at file scope due to (void *)0 == (sem_t *)0?

[Sebastian Huber <sebastian.huber@embedded-brains.de>]

Hello,

I use a typedef for static assertions for pre C11 compilers. For one 
static assertion

typedef struct { int i; } sem_t;

typedef int static_assert_sem_failed [((void *)0 == (sem_t *)0) ? 1 : -1];

_Static_assert((void *)0 == (sem_t *)0, "sem_failed");

I get a warning like this:

gcc -S -o - sa.c > /dev/null
sa.c:3:1: warning: variably modified ‘static_assert_sem_failed’ at file 
scope
  typedef int static_assert_sem_failed [((void *)0 == (sem_t *)0) ? 1 : -1];
  ^~~~~~~

Is there some way to get around this warning? The same expression in the 
_Static_assert() doen't lead to a warning.

-- 
Sebastian Huber, embedded brains GmbH

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