Tools: Don't install libc6-i386 on 32bit Ubuntu

Tools/scripts/install-prereqs-ubuntu.sh

@@ -7,7 +7,7 @@ BASE_PKGS="build-essential ccache g++ gawk git make wget"
 PYTHON_PKGS="future lxml pymavlink MAVProxy"
 PX4_PKGS="python-argparse openocd flex bison libncurses5-dev \
           autoconf texinfo libftdi-dev zlib1g-dev \
-          zip genromfs python-empy libc6-i386 cmake cmake-data"
+          zip genromfs python-empy cmake cmake-data"
 ARM_LINUX_PKGS="g++-arm-linux-gnueabihf pkg-config-arm-linux-gnueabihf"
 SITL_PKGS="libtool libxml2-dev libxslt1-dev python-dev python-pip python-setuptools python-matplotlib python-serial python-scipy python-opencv python-numpy python-pyparsing realpath"
 ASSUME_YES=false
@@ -27,6 +27,13 @@ if [ "$yrelease" -ge "$UBUNTU_YEAR" ]; then
     fi
 fi
 
+MACHINE_TYPE=$(uname -m)
+if [ ${MACHINE_TYPE} == 'x86_64' ]; then
+    PX4_PKGS+=" libc6-i386"
+else
+  # 32-bit stuff here
+fi
+
 # GNU Tools for ARM Embedded Processors
 # (see https://launchpad.net/gcc-arm-embedded/)
 ARM_ROOT="gcc-arm-none-eabi-4_9-2015q3"