fix(driver): compile support for s390 compat support conditionally

Commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8e0b986c59c67e08ada646249f834655a9e6da16
removed 31-bit code support for s390 and any related macro, so compile
out from kmod the check involving the usage of the dropped
`_TIF_31BIT` macro if this is not available on the kernel against
which we compile.

Signed-off-by: Leonardo Di Giovanna <leonardodigiovanna1@gmail.com>

Author: ekoops

driver/configure/COMPAT_S390/test.c

@@ -0,0 +1,28 @@
+/*
+
+Copyright (C) 2026 The Falco Authors.
+
+This file is dual licensed under either the MIT or GPL 2. See MIT.txt
+or GPL2.txt for full copies of the license.
+
+*/
+
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/thread_info.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("the Falco authors");
+
+static int compat_s390_init(void) {
+#ifdef CONFIG_S390
+	unsigned long flags = task_thread_info(current)->flags & _TIF_31BIT;
+	(void)flags;
+#endif /* CONFIG_S390 */
+	return 0;
+}
+
+static void compat_s390_exit(void) {}
+
+module_init(compat_s390_init);
+module_exit(compat_s390_exit);

driver/main.c

@@ -1976,7 +1976,7 @@ static inline bool kmod_in_ia32_syscall(void) {
 #elif defined(CONFIG_ARM64)
 	if(unlikely(task_thread_info(current)->flags & _TIF_32BIT))
 		return true;
-#elif defined(CONFIG_S390)
+#elif defined(CONFIG_S390) && HAS_COMPAT_S390
 	if(unlikely(task_thread_info(current)->flags & _TIF_31BIT))
 		return true;
 #elif defined(CONFIG_PPC64)