configure.ac: add aarch64 to list of registerised

Similar to 'arm' 'aarch64' has working llvm codegen,
no need to fallback to unregisterised buld by default.
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

configure.ac

@@ -242,7 +242,7 @@ AC_SUBST(SOLARIS_BROKEN_SHLD)
 dnl ** Do an unregisterised build?
 dnl --------------------------------------------------------------
 case "$TargetArch" in
-    i386|x86_64|powerpc|powerpc64|powerpc64le|arm)
+    i386|x86_64|powerpc|powerpc64|powerpc64le|arm|aarch64)
         UnregisterisedDefault=NO
         ;;
     *)