sys/prctl.h: add PR_SET_SYSCALL_USER_DISPATCH from linux v5.11

see

  linux commit 1446e1df9eb183fdf81c3f0715402f1d7595d4cb
  kernel: Implement selective syscall userspace redirection

  linux commit 36a6c843fd0d8e02506681577e96dabd203dd8e8
  entry: Use different define for selector variable in SUD

redirect syscalls to a userspace handler via SIGSYS, except for a specific
range of code. can be toggled via a memory write to a selector variable.
mainly for wine.

include/sys/prctl.h

@@ -168,6 +168,12 @@ struct prctl_mm_map {
 #define PR_SET_IO_FLUSHER 57
 #define PR_GET_IO_FLUSHER 58
 
+#define PR_SET_SYSCALL_USER_DISPATCH 59
+#define PR_SYS_DISPATCH_OFF 0
+#define PR_SYS_DISPATCH_ON 1
+#define SYSCALL_DISPATCH_FILTER_ALLOW 0
+#define SYSCALL_DISPATCH_FILTER_BLOCK 1
+
 int prctl (int, ...);
 
 #ifdef __cplusplus