For gcc 4.6 and newer, _Static_assert is a keyword, so don't try to

redefine it. It does what we want, and is always available unlike
other alternatives.

sys/conf/kern.mk

@@ -38,7 +38,7 @@ CWARNEXTRA?=	-Wno-error-tautological-compare -Wno-error-empty-body \
 # building with gcc 4.8 and newer. Nothing older has been tested.
 CWARNEXTRA?=	-Wno-error=inline -Wno-error=enum-compare -Wno-error=unused-but-set-variable \
 		-Wno-error=aggressive-loop-optimizations -Wno-error=maybe-uninitialized \
-		-Wno-error=unused-local-typedefs -Wno-error=array-bounds -Wno-error=address \
+		-Wno-error=array-bounds -Wno-error=address \
 		-Wno-error=cast-qual -Wno-error=sequence-point -Wno-error=attributes
 .endif
 

sys/sys/cdefs.h

@@ -288,6 +288,8 @@
 #if (defined(__cplusplus) && __cplusplus >= 201103L) || \
     __has_extension(cxx_static_assert)
 #define	_Static_assert(x, y)	static_assert(x, y)
+#elif __GNUC_PREREQ__(4,6)
+/* Nothing, gcc 4.6 and higher has _Static_assert built-in */
 #elif defined(__COUNTER__)
 #define	_Static_assert(x, y)	__Static_assert(x, __COUNTER__)
 #define	__Static_assert(x, y)	___Static_assert(x, y)