feat: detect proc_ops support via header parsing instead of version check. (#411)

Some kernels (e.g. 5.4 with backports) include proc_ops despite being
older than 5.6.0. Replace hardcoded version check with runtime header
detection to handle these cases.

- Check for "struct proc_ops" in include/linux/proc_fs.h
- Use KSU_COMPAT_HAS_PROC_OPS macro for conditional compilation
- Fixes build failures on kernels with backported proc_ops

Signed-off-by: JackAltman

kernel/Makefile

@@ -180,4 +180,9 @@ else
 $(info -- You have not integrated susfs in your kernel yet.)
 $(info -- Read: https://gitlab.com/simonpunk/susfs4ksu)
 endif
+
+# Function proc_ops check
+ifeq ($(shell grep -q "struct proc_ops " $(srctree)/include/linux/proc_fs.h; echo $$?),0)
+ccflags-y += -DKSU_COMPAT_HAS_PROC_OPS
+endif
 # Keep a new line here!! Because someone may append config