aarch64: fix build with missing NT_ARM_PAC_ENABLED_KEYS

On a RHEL 8 based system building CRIU fails with:

criu/arch/aarch64/crtools.c: In function 'save_pac_keys':
criu/arch/aarch64/crtools.c:73:39: error: 'NT_ARM_PAC_ENABLED_KEYS' undeclared (first use in this function); did you mean 'NT_ARM_PACA_KEYS'?
   ret = ptrace(PTRACE_GETREGSET, pid, NT_ARM_PAC_ENABLED_KEYS, &iov);
                                       ^~~~~~~~~~~~~~~~~~~~~~~
                                       NT_ARM_PACA_KEYS
criu/arch/aarch64/crtools.c:73:39: note: each undeclared identifier is reported only once for each function it appears in
criu/arch/aarch64/crtools.c: In function 'arch_ptrace_restore':
criu/arch/aarch64/crtools.c:261:44: error: 'NT_ARM_PAC_ENABLED_KEYS' undeclared (first use in this function); did you mean 'NT_ARM_PACA_KEYS'?
   if ((ret = ptrace(PTRACE_SETREGSET, pid, NT_ARM_PAC_ENABLED_KEYS, &iov))) {
                                            ^~~~~~~~~~~~~~~~~~~~~~~
                                            NT_ARM_PACA_KEYS

This adds the missing define if it is undefined.

Signed-off-by: Adrian Reber <areber@redhat.com>

Author: adrianreber

criu/arch/aarch64/crtools.c

@@ -23,6 +23,10 @@
 #include "compel/infect.h"
 #include "pstree.h"
 
+#ifndef NT_ARM_PAC_ENABLED_KEYS
+#define NT_ARM_PAC_ENABLED_KEYS	0x40a	/* AArch64 pointer authentication enabled keys. */
+#endif
+
 extern unsigned long getauxval(unsigned long type);
 
 #define assign_reg(dst, src, e) dst->e = (__typeof__(dst->e))(src)->e