RTEMS: Add multilib configuration for aarch64

Add a multilib with workarounds for Cortex-A53 errata.

gcc/ChangeLog:

	* config.gcc (aarch64-*-rtems*): Add target makefile fragment
	t-aarch64-rtems.
	* config/aarch64/t-aarch64-rtems: New file.

Author: sebhub

gcc/config.gcc

@@ -1199,6 +1199,7 @@ aarch64*-*-elf | aarch64*-*-fuchsia* | aarch64*-*-rtems*)
                 ;;
 	aarch64-*-rtems*)
 		tm_file="${tm_file} aarch64/rtems.h rtems.h"
+		tmake_file="${tmake_file} aarch64/t-aarch64-rtems"
 		;;
 	esac
 	case $target in

gcc/config/aarch64/t-aarch64-rtems

@@ -0,0 +1,42 @@
+# Multilibs for aarch64 RTEMS targets.
+#
+# Copyright (C) 2024 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/>.
+
+MULTILIB_OPTIONS  =
+MULTILIB_DIRNAMES =
+MULTILIB_REQUIRED =
+
+MULTILIB_OPTIONS  += mabi=ilp32
+MULTILIB_DIRNAMES += ilp32
+
+MULTILIB_OPTIONS  += mno-outline-atomics
+MULTILIB_DIRNAMES += nooa
+
+MULTILIB_OPTIONS  += mcpu=cortex-a53
+MULTILIB_DIRNAMES += a53
+
+MULTILIB_OPTIONS  += mfix-cortex-a53-835769
+MULTILIB_DIRNAMES += fix835769
+
+MULTILIB_OPTIONS  += mfix-cortex-a53-843419
+MULTILIB_DIRNAMES += fix843419
+
+MULTILIB_REQUIRED += mabi=ilp32
+MULTILIB_REQUIRED += mabi=ilp32/mno-outline-atomics/mcpu=cortex-a53/mfix-cortex-a53-835769/mfix-cortex-a53-843419
+MULTILIB_REQUIRED += mno-outline-atomics/mcpu=cortex-a53/mfix-cortex-a53-835769/mfix-cortex-a53-843419