Fix objtool: missing int3 after ret warning

Resolve straight-line speculation warnings reported by objtool
for x86_64 assembly on Linux when CONFIG_SLS is set.  See the
following LWN article for the complete details.

https://lwn.net/Articles/877845/

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #13528
Closes #13575

module/lua/setjmp/setjmp_x86_64.S

@@ -35,6 +35,12 @@ x:
 	.size	x, [.-x]
 
 
+#if defined(__linux__) && defined(CONFIG_SLS)
+#define	RET	ret; int3
+#else
+#define	RET	ret
+#endif
+
 /*
  * Setjmp and longjmp implement non-local gotos using state vectors
  * type label_t.
@@ -52,7 +58,7 @@ x:
 	movq	0(%rsp), %rdx		/* return address */
 	movq	%rdx, 56(%rdi)		/* rip */
 	xorl	%eax, %eax		/* return 0 */
-	ret
+	RET
 	SET_SIZE(setjmp)
 
 	ENTRY(longjmp)
@@ -67,7 +73,7 @@ x:
 	movq	%rdx, 0(%rsp)
 	xorl	%eax, %eax
 	incl	%eax			/* return 1 */
-	ret
+	RET
 	SET_SIZE(longjmp)
 
 #ifdef __ELF__