sys/prctl.h: add PR_*_TAGGED_ADDR_* from linux v5.4

per thread prctl commands to relax the syscall abi such that top bits
of user pointers are ignored in the kernel. this allows the use of
those bits by hwasan or by mte to color pointers and memory on aarch64:

  linux commit 63f0c60379650d82250f22e4cf4137ef3dc4f43d
  arm64: Introduce prctl() options to control the tagged user addresses ABI

include/sys/prctl.h

@@ -154,6 +154,10 @@ struct prctl_mm_map {
 #define PR_PAC_APDBKEY (1UL << 3)
 #define PR_PAC_APGAKEY (1UL << 4)
 
+#define PR_SET_TAGGED_ADDR_CTRL 55
+#define PR_GET_TAGGED_ADDR_CTRL 56
+#define PR_TAGGED_ADDR_ENABLE (1UL << 0)
+
 int prctl (int, ...);
 
 #ifdef __cplusplus