Add support for Semihosting v2 support for AArch64 in libgloss.

Semihosting v2 changes are documented here:
https://developer.arm.com/docs/100863/latest/

The biggest change is the addition of an extensions mechanism
to add more extensions in the future.

Signed-off-by: Tamar Christina <tamar.christina@arm.com>

libgloss/aarch64/_kill.c

@@ -45,5 +45,11 @@ _kill (int pid, int sig)
 
   block[0] = ADP_Stopped_RunTimeError;
   block[1] = sig;
-  return do_AngelSVC (AngelSVC_Reason_ReportException, block);
+
+#if SEMIHOST_V2
+  if (_has_ext_exit_extended ())
+    return do_AngelSVC (AngelSVC_Reason_ReportExceptionExtended, block);
+  else
+#endif
+    return do_AngelSVC (AngelSVC_Reason_ReportException, block);
 }