Documentation updates
Build process update: make clang link against our new libstdc++

Previously it would always link against the system libstdc++; not sure how
that was working.

Also, put that in its own included makefile so that we can track the dependence
on the configuration parameters (otherwise you would have to run a configuration
manually to get this change).
Rebase LLVM rev
Merge remote-tracking branch 'upstream/master'