teach gcc about arn64-apple-darwin hosts

gcc/gcc/config.host

@@ -263,6 +263,10 @@ case ${host} in
     out_host_hook_obj="${out_host_hook_obj} host-ppc64-darwin.o"
     host_xmake_file="${host_xmake_file} rs6000/x-darwin64"
     ;;
+  arm-*-darwin*)
+    out_host_hook_obj="${out_host_hook_obj} host-aarch64-darwin.o"
+    host_xmake_file="${host_xmake_file} aarch64/x-darwin"
+    ;;
   rs6000-ibm-aix* | powerpc-ibm-aix*)
     host_xmake_file="${host_xmake_file} rs6000/x-aix"
     ;;

gcc/gcc/config/aarch64/host-aarch64-darwin.c

@@ -0,0 +1,32 @@
+/* i386-darwin host-specific hook definitions.
+   Copyright (C) 2003-2019 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#define IN_TARGET_CODE 1
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "hosthooks.h"
+#include "hosthooks-def.h"
+#include "config/host-darwin.h"
+
+/* Darwin doesn't do anything special for aarch64 hosts; this file exists just
+   to include config/host-darwin.h.  */
+
+const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;

gcc/gcc/config/aarch64/x-darwin

@@ -0,0 +1,3 @@
+host-aarch64-darwin.o : $(srcdir)/config/aarch64/host-aarch64-darwin.c
+	$(COMPILE) $<
+	$(POSTCOMPILE)

gcc/gcc/config/host-darwin.c

@@ -24,7 +24,7 @@
 #include "config/host-darwin.h"
 
 /* Yes, this is really supposed to work.  */
-static char pch_address_space[1024*1024*1024] __attribute__((aligned (4096)));
+static char pch_address_space[1024*1024*1024] __attribute__((aligned (16384)));
 
 /* Return the address of the PCH address space, if the PCH will fit in it.  */