Move xvfb. Add llvmpipe.so.

third_party/xvfb/building/install-prereq

 #!/bin/sh
 # 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.
 
 # This is a convenience for installing prerequisites that seem to be often
 # missing.
 
 PPATH=/usr/lib/pkgconfig
 LPATH="$(pwd)"
 export PKG_CONFIG_PATH="${PPATH}"
 
 function getxfromy() {
-  if [ \! -f "${PPATH}"/"$1".pc ] ; then
+  case "$1" in
+    */*) testpath="$1" ;;
+    *) testpath="${PPATH}"/"$1".pc ;;
+  esac
+  if [ \! -f "${testpath}" ] ; then
     sudo apt-get install "$2"
   fi
 }
 
 getxfromy pixman-1 libpixman-1-dev
 getxfromy fixesproto x11proto-fixes-dev
 getxfromy damageproto x11proto-damage-dev
 getxfromy xcmiscproto x11proto-xcmisc-dev
 getxfromy bigreqsproto x11proto-bigreqs-dev
 getxfromy randrproto x11proto-randr-dev
 getxfromy renderproto x11proto-render-dev
 getxfromy fontsproto x11proto-fonts-dev
 getxfromy videoproto x11proto-video-dev
 getxfromy compositeproto x11proto-composite-dev
 getxfromy scrnsaverproto x11proto-scrnsaver-dev
 getxfromy resourceproto x11proto-resource-dev
 getxfromy xineramaproto x11proto-xinerama-dev
 getxfromy pciaccess libpciaccess-dev
 getxfromy gl libgl1-mesa-dev
 getxfromy glproto x11proto-gl-dev
 getxfromy xf86driproto x11proto-xf86dri-dev
 getxfromy fontenc libfontenc-dev
 getxfromy makedepend xutils-dev
 getxfromy talloc libfontenc-dev
 getxfromy autoconf autoconf
 getxfromy libtool libtool
+getxfromy ffi ffi-dev
+getxfromy /usr/bin/llvm-config llvm-dev