AArch64: Linker64 support for AArch64

Addition of support for AArch64 in the linker64 target.

Change-Id: I8dfd9711278f6706063e91f626b6007ea7a3dd6e
Signed-off-by: Marcus Oakland <marcus.oakland@arm.com>

linker/linker_phdr.cpp

@@ -29,6 +29,7 @@
 #include "linker_phdr.h"
 
 #include <errno.h>
+#include <machine/exec.h>
 #include <sys/mman.h>
 
 #include "linker.h"
@@ -201,17 +202,7 @@ bool ElfReader::VerifyElfHeader() {
     return false;
   }
 
-  if (header_.e_machine !=
-#if defined(__arm__)
-      EM_ARM
-#elif defined(__i386__)
-      EM_386
-#elif defined(__mips__)
-      EM_MIPS
-#elif defined(__x86_64__)
-      EM_X86_64
-#endif
-  ) {
+  if (header_.e_machine != ELF_TARG_MACH) {
     DL_ERR("\"%s\" has unexpected e_machine: %d", name_, header_.e_machine);
     return false;
   }