ARM64: Add support for ARM64e pointer authentication codes (PAC).

Contributed by Peter Cawley. #559

src/lj_arch.h

@@ -259,6 +259,9 @@
 #define LJ_ARCH_NAME		"arm64"
 #define LJ_ARCH_ENDIAN		LUAJIT_LE
 #endif
+#if !defined(LJ_ABI_PAUTH) && defined(__arm64e__)
+#define LJ_ABI_PAUTH		1
+#endif
 #define LJ_TARGET_ARM64		1
 #define LJ_TARGET_EHRETREG	0
 #define LJ_TARGET_EHRAREG	30
@@ -603,6 +606,10 @@
 #define LJ_SOFTFP		(!LJ_ARCH_HASFPU)
 #define LJ_SOFTFP32		(LJ_SOFTFP && LJ_32)
 
+#ifndef LJ_ABI_PAUTH
+#define LJ_ABI_PAUTH		0
+#endif
+
 #if LJ_ARCH_ENDIAN == LUAJIT_BE
 #define LJ_LE			0
 #define LJ_BE			1