kernel: add __poll_t compat for pre-4.16 and backported kernels (#194)

__poll_t was introduced in v4.16-rc1. Add Makefile header check to detect and provide fallback for older kernels and those with backports.

Signed-off-by: AzyrRuthless <azyrruthless@tutamail.com>

kernel/file_wrapper.c

@@ -20,6 +20,10 @@
 
 #include "file_wrapper.h"
 
+#ifdef KSU_NEED_POLL_T_DEF
+typedef unsigned __bitwise __poll_t;
+#endif
+
 static loff_t mksu_wrapper_llseek(struct file *fp, loff_t off, int flags)
 {
 	struct ksu_file_wrapper *data = fp->private_data;