Building druntime/Phobos for D2

LDC currently needs custom forks of druntime and Phobos. They are integrated
with the main repository using Git submodules. To build them, make sure you
have up-to-date copies of the submodules in your local repository:

$ git submodule update -i

The libraries should then be built and installed automatically along with the
compiler itself. If, for some reason, you want to build them separately, the
targets are:

$ make runtime
$ make phobos2

Building Tango for D1

This directory used to contain scripts for building Tango for LDC/D1, which
became obsolete after LDC support was added to its build system, and were
consequently removed. Please use the official Tango build system (bob) from
now on.