Support for clang specific boost and protobuf dirs:

Clang does not understand gcc 5's new ABI. On linux systems
that default to the new ABI (such as ubuntu 15.10), building
with clang requires using C++ libraries built with the the old
gcc ABI.

When building with the clang protobuf lib, a common error is to
load the gcc protobuf library at run time. When set, PROTOBUF_ROOT
is added to rpath to make sure the correct lib is loaded.

Adds a script to install clang and download and build boost and
protobuf with boost.

Builds/Ubuntu/build_clang_libs.sh

@@ -0,0 +1,79 @@
+#!/usr/bin/env bash
+
+#
+# This scripts installs boost and protobuf built with clang. This is needed on
+# ubuntu 15.10 when building with clang
+# It will build these in a 'clang' subdirectory that it creates below the directory
+# this script is run from. If a clang directory already exists the script will refuse
+# to run.
+
+if hash lsb_release 2>/dev/null; then
+    if [ $(lsb_release -si) == "Ubuntu" ]; then
+        ubuntu_release=$(lsb_release -sr)
+    fi
+fi
+
+if [ -z "${ubuntu_release}" ]; then
+    echo "System not supported"
+    exit 1
+fi
+
+if ! hash clang 2>/dev/null; then
+    clang_version=3.7
+    sudo apt-get -y install clang-${clang_version}
+    update-alternatives --install /usr/bin/clang clang /usr/bin/clang-${clang_version} 99 clang++
+    hash -r
+    if ! hash clang 2>/dev/null; then
+        echo "Please install clang"
+        exit 1
+    fi
+fi
+
+if [ ${ubuntu_release} != "15.10" ]; then
+    echo "clang specific boost and protobuf not needed"
+    exit 0
+fi
+
+if [ -d clang ]; then
+    echo "clang directory already exists. Cowardly refusing to run"
+    exit 1
+fi
+
+if ! hash wget 2>/dev/null; then
+    sudo apt-get -y install wget
+    hash -r
+    if ! hash wget 2>/dev/null; then
+        echo "Please install wget"
+        exit 1
+    fi
+fi
+
+num_procs=$(lscpu -p | grep -v '^#' | sort -u -t, -k 2,4 | wc -l) # pysical cores
+
+mkdir clang
+pushd clang > /dev/null
+
+# Install protobuf
+pb=protobuf-2.6.1
+pb_tar=${pb}.tar.gz 
+wget -O ${pb_tar} https://github.com/google/protobuf/releases/download/v2.6.1/${pb_tar}
+tar xf ${pb_tar}
+rm ${pb_tar}
+pushd ${pb} > /dev/null
+./configure CC=clang CXX=clang++ CXXFLAGS='-std=c++14 -O3 -g'
+make -j${num_procs}
+popd > /dev/null
+
+# Install boost
+boost_ver=1.60.0
+bd=boost_${boost_ver//./_}
+bd_tar=${bd}.tar.gz
+wget -O ${bd_tar} http://sourceforge.net/projects/boost/files/boost/${boost_ver}/${bd_tar}
+tar xf ${bd_tar}
+rm ${bd_tar}
+pushd ${bd} > /dev/null
+./bootstrap.sh
+./b2 toolset=clang -j${num_procs}
+popd > /dev/null
+
+popd > /dev/null