macro.h: include assert.h so that static_assert can be properly checked for

For the definition of assert_cc() we try to use static_assert and check
for it with "#ifdef". But that can only work if assert.h is imported
before. Hence let's do so.

src/basic/macro.h

@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 #pragma once
 
+#include <assert.h>
 #include <inttypes.h>
 #include <stdbool.h>
 #include <sys/param.h>