libc: Add variadic assert in accordance with C23

Signed-off-by: Faraz Vahedi <kfv@kfv.io>

Author: kfv

include/assert.h

@@ -36,6 +36,8 @@
 
 #include <sys/cdefs.h>
 
+#include <stdbool.h>
+
 /*
  * Unlike other ANSI header files, <assert.h> may usefully be included
  * multiple times, with and without NDEBUG defined.
@@ -46,16 +48,17 @@
 #undef __assert_unreachable
 
 #ifdef NDEBUG
-#define	assert(e)	((void)0)
-#define	_assert(e)	((void)0)
+#define	assert(...)	((void)0)
+#define	_assert(...)	((void)0)
 #if __BSD_VISIBLE
 #define	__assert_unreachable()	__unreachable()
 #endif	/* __BSD_VISIBLE */
 #else
-#define	_assert(e)	assert(e)
-
-#define	assert(e)	((e) ? (void)0 : __assert(__func__, __FILE__, \
-			    __LINE__, #e))
+#define	assert(...)	((void)sizeof(((bool(*)(bool))0)(__VA_ARGS__)),  \
+			    (__VA_ARGS__) ? (void)0 :                    \
+			    __assert(__func__, __FILE__,                 \
+			    __LINE__, #__VA_ARGS__))
+#define	_assert(...)	assert(__VA_ARGS__)
 #if __BSD_VISIBLE
 #define	__assert_unreachable()	assert(0 && "unreachable segment reached")
 #endif	/* __BSD_VISIBLE */