diff -urN gcc-4.9.2/gcc/config/i386/t-elf64 gcc-4.9.2/gcc/config/i386/t-elf64
--- gcc-4.9.2/gcc/config/i386/t-elf64	1969-12-31 16:00:00.000000000 -0800
+++ gcc-4.9.2/gcc/config/i386/t-elf64	2015-06-17 11:20:08.032513005 -0700
@@ -0,0 +1,38 @@
+# Copyright (C) 2002-2014 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/>.
+
+# On Debian, Ubuntu and other derivative distributions, the 32bit libraries
+# are found in /lib32 and /usr/lib32, /lib64 and /usr/lib64 are symlinks to
+# /lib and /usr/lib, while other distributions install libraries into /lib64
+# and /usr/lib64.  The LSB does not enforce the use of /lib64 and /usr/lib64,
+# it doesn't tell anything about the 32bit libraries on those systems.  Set
+# MULTILIB_OSDIRNAMES according to what is found on the target.
+
+# To support i386, x86-64 and x32 libraries, the directory structrue
+# should be:
+#
+# 	/lib has i386 libraries.
+# 	/lib64 has x86-64 libraries.
+# 	/libx32 has x32 libraries.
+#
+comma=,
+MULTILIB_OPTIONS    = $(subst $(comma),/,$(TM_MULTILIB_CONFIG))
+MULTILIB_DIRNAMES   = $(patsubst m%, %, $(subst /, ,$(MULTILIB_OPTIONS)))
+MULTILIB_OSDIRNAMES = m64=../lib64$(call if_multiarch,:x86_64-elf)
+MULTILIB_OSDIRNAMES+= m32=$(if $(wildcard $(shell echo $(SYSTEM_HEADER_DIR))/../../usr/lib32),../lib32,../lib)$(call if_multiarch,:i386-elf)
+MULTILIB_OSDIRNAMES+= mx32=../libx32$(call if_multiarch,:x86_64-elf-x32)
diff -urN gcc-4.9.2/gcc/config.gcc gcc-4.9.2/gcc/config.gcc
--- gcc-4.9.2/gcc/config.gcc	2015-06-17 11:20:57.841008182 -0700
+++ gcc-4.9.2/gcc/config.gcc	2015-06-17 11:17:24.818890200 -0700
@@ -1353,6 +1353,30 @@
 	;;
 x86_64-*-elf*)
 	tm_file="${tm_file} i386/unix.h i386/att.h dbxelf.h elfos.h newlib-stdint.h i386/i386elf.h i386/x86-64.h"
+	tmake_file="${tmake_file} i386/t-elf64"
+	x86_multilibs="${with_multilib_list}"
+	if test "$x86_multilibs" = "default"; then
+		case ${with_abi} in
+		x32 | mx32)
+			x86_multilibs="mx32"
+			;;
+		*)
+			x86_multilibs="m64,m32"
+			;;
+		esac
+	fi
+	x86_multilibs=`echo $x86_multilibs | sed -e 's/,/ /g'`
+	for x86_multilib in ${x86_multilibs}; do
+		case ${x86_multilib} in
+		m32 | m64 | mx32)
+			TM_MULTILIB_CONFIG="${TM_MULTILIB_CONFIG},${x86_multilib}"
+			;;
+		*)
+			echo "--with-multilib-list=${x86_with_multilib} not supported."
+			exit 1
+		esac
+	done
+	TM_MULTILIB_CONFIG=`echo $TM_MULTILIB_CONFIG | sed 's/^,//'`
 	;;
 i[34567]86-*-rdos*)
     tm_file="${tm_file} i386/unix.h i386/att.h dbxelf.h elfos.h newlib-stdint.h i386/i386elf.h i386/rdos.h"