Only install the 32-bit compat packages on 64-bit.

build/install-build-deps.sh

 #!/bin/bash -e
 
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Script to install everything needed to build chromium (well, ideally, anyway)
 # See http://code.google.com/p/chromium/wiki/LinuxBuildInstructions
 # and http://code.google.com/p/chromium/wiki/LinuxBuild64Bit
 
@@ skipping 49 matching lines @@
           language-pack-fr libapache2-mod-php5 libasound2-dev libbz2-dev
           libcairo2-dev libcups2-dev libcurl4-gnutls-dev libdbus-glib-1-dev
           libelf-dev libgconf2-dev libgl1-mesa-dev libglib2.0-dev
           libglu1-mesa-dev libgnome-keyring-dev libgtk2.0-dev
           libkrb5-dev libnspr4-dev libnss3-dev libpam0g-dev libsctp-dev
           libsqlite3-dev libssl-dev libudev-dev libwww-perl libxslt1-dev
           libxss-dev libxt-dev libxtst-dev mesa-common-dev patch
           perl php5-cgi pkg-config python python-cherrypy3 python-dev
           python-psutil rpm ruby subversion ttf-dejavu-core ttf-indic-fonts
           ttf-kochi-gothic ttf-kochi-mincho ttf-thai-tlwg wdiff git-core
-          libc6-i386 lib32gcc1
           $chromeos_dev_list"
 
+# 64-bit systems need a minimum set of 32-bit compat packages for the pre-built
+# NaCL binaries. These are always needed, regardless of whether or not we want
+# the full 32-bit "cross-compile" support (--lib32).
+if [ "$(uname -m)" = "x86_64" ]; then
+  dev_list="${dev_list} libc6-i386 lib32gcc1"
+fi
+
 # Run-time libraries required by chromeos only
 chromeos_lib_list="libpulse0 libbz2-1.0 libcurl4-gnutls-dev"
 
 # Full list of required run-time libraries
 lib_list="libatk1.0-0 libc6 libasound2 libcairo2 libcups2 libdbus-glib-1-2
           libexpat1 libfontconfig1 libfreetype6 libglib2.0-0 libgnome-keyring0
           libgtk2.0-0 libpam0g libpango1.0-0 libpcre3 libpixman-1-0
           libpng12-0 libstdc++6 libsqlite3-0 libudev0 libx11-6 libxau6 libxcb1
           libxcomposite1 libxcursor1 libxdamage1 libxdmcp6 libxext6 libxfixes3
           libxi6 libxinerama1 libxrandr2 libxrender1 libxtst6 zlib1g
@@ skipping 316 matching lines @@
              sed -e 's/[.]so[.][0-9].*/.so/' |
              sort -u); do
     [ "x${i##*/}" = "xld-linux.so" ] && continue
     [ -r "$i" ] && continue
     j="$(ls "$i."* | sed -e 's/.*[.]so[.]\([^.]*\)$/\1/;t;d' |
          sort -n | tail -n 1)"
     [ -r "$i.$j" ] || continue
     sudo ln -s "${i##*/}.$j" "$i"
   done
 fi