ck: recognize _KERNEL on Linux cross-builds

Use the Linux kernel header path when either __KERNEL__ or _KERNEL is defined so Ubuntu-based cross-builds do not fall back to missing hosted headers like limits.h and stdint.h.

AI-Assisted-by: OpenAI Codex (GPT-5)
Signed-off-by: Lucas Holt <luke@foolishgames.com>

Author: laffer1

sys/contrib/ck/include/ck_limits.h

@@ -24,7 +24,7 @@
  * SUCH DAMAGE.
  */
 
-#if defined(__linux__) && defined(__KERNEL__)
+#if defined(__linux__) && (defined(__KERNEL__) || defined(_KERNEL))
 #include <linux/kernel.h>
 
 #ifndef UINT8_MAX
@@ -45,4 +45,4 @@
 #include <sys/limits.h>
 #else
 #include <limits.h>
-#endif /* __linux__ && __KERNEL__ */
+#endif /* __linux__ && (__KERNEL__ || _KERNEL) */

sys/contrib/ck/include/ck_stdint.h

@@ -24,11 +24,11 @@
  * SUCH DAMAGE.
  */
 
-#if defined(__linux__) && defined(__KERNEL__)
+#if defined(__linux__) && (defined(__KERNEL__) || defined(_KERNEL))
 #include <linux/kernel.h>
 #include <linux/types.h>
 #elif defined(__MidnightBSD__) && defined(_KERNEL)
 #include <sys/stdint.h>
 #else
 #include <stdint.h>
-#endif /* __linux__ && __KERNEL__ */
+#endif /* __linux__ && (__KERNEL__ || _KERNEL) */