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.
