fixes #238 improve Debug linking time by building LLVM -O3
-this significantly reduces the size of the resulting object files
cmake automatically use ccache if found
fixes #238 cmake automatically use ld.gold for linking
src/runtime/inline/* and pass -Btools/build_system for using gold
otherwise
fixes #238 update INSTALLING.md for cmake on Ubuntu 12.04 and 14.04
Merge pull request #242 from dagar/cmake

fixes #238 CMake issues