common/sfc_efx/base: use C11 static assert

[ upstream commit 047d7032b76a226f2f1c36775688950933f9121b ]

The sfc base code had its own definition of static assertions
using the out of bound array access hack. Replace it with a
static_assert like rte_common.h.

The use of null pointer to compute offset is not always a constant
in older versions of clang. Use standard offsetof() instead.

Fixes: f67e471 ("net/sfc/base: fix coding style")

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>

drivers/common/sfc_efx/base/efx.h

@@ -7,6 +7,8 @@
 #ifndef	_SYS_EFX_H
 #define	_SYS_EFX_H
 
+#include <assert.h>
+
 #include "efx_annote.h"
 #include "efsys.h"
 #include "efx_types.h"
@@ -17,14 +19,20 @@
 extern "C" {
 #endif
 
-#define	EFX_STATIC_ASSERT(_cond)		\
-	((void)sizeof (char[(_cond) ? 1 : -1]))
+/*
+ * Triggers an error at compilation time if the condition is false.
+ *
+ * The  { } exists to workaround a bug in clang (#55821)
+ * where it would not handle _Static_assert in a switch case.
+ */
+#define	EFX_STATIC_ASSERT(_cond) \
+	{ static_assert((_cond), #_cond); }
 
 #define	EFX_ARRAY_SIZE(_array)			\
 	(sizeof (_array) / sizeof ((_array)[0]))
 
 #define	EFX_FIELD_OFFSET(_type, _field)		\
-	((size_t)&(((_type *)0)->_field))
+	offsetof(_type, _field)
 
 /* The macro expands divider twice */
 #define	EFX_DIV_ROUND_UP(_n, _d)		(((_n) + (_d) - 1) / (_d))