Address objtool check failures in lua module

The use of void __attribute__((noreturn)) in kernel builds
was causing lots of warnings if CONFIG_STACK_VALIDATION
is active. For now we just remove this attribute to achieve
clean builds for the Lua module. There was no significant
increase in the time to run the full channel_program ZTS tests.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Don Brady <don.brady@delphix.com>
Closes #7173

module/lua/llimits.h

@@ -97,8 +97,10 @@ typedef LUAI_UACNUMBER l_uacNumber;
 
 /*
 ** non-return type
+**
+** Supress noreturn attribute in kernel builds to avoid objtool check warnings
 */
-#if defined(__GNUC__)
+#if defined(__GNUC__) && !defined(_KERNEL)
 #define l_noret		void __attribute__((noreturn))
 #elif defined(_MSC_VER)
 #define l_noret		void __declspec(noreturn)