Fix mclinker build based on the current merge point (6824c79120).

* Add missing lib/LD/IdenticalCodeFolding.cpp and compile it.
* Compile lib/Support/Demangle.cpp
* Merge point:
    commit 6824c791204cf5daabdfe008ee8808799f348815
    Author: Pete Chou <petechou@gmail.com>
    Date:   Tue Jul 15 10:15:12 2014 +0800

        Fix typo in README.

Change-Id: I1085d76ac015fc88e7daa6093b53758efa0794b6
Signed-off-by: Pete Chou <pete.chou@gmail.com>