Make official ChakraCore Linux binaries that work on all currently maintained versions of Linux

This is is a follow on from https://github.com/Microsoft/ChakraCore/issues/2278 . The currently available Linux ChakraCore binaries only work on some Linux distros. Ideally they would work on all (currently maintained) Linux distros.

I've put together a rough build system that is capable of generating such binaries (https://github.com/cosinusoidally/ChakraCore-experiments/tree/master/build-chakracore). It does this by generating a CentOS 6 based root filesystem, and building a copy of CMake 3.5.2 and Clang 3.8. It then uses CMake and Clang to build ChakraCore. Unfortunately there are still one or two manual steps since ChakraCore's CMakeFiles do not instruct the compiler to link to librt. I'm sure that would be easy to patch, but my knowledge of CMake is quite limited. My current work around is to manually invoke the compiler with "-lrt" appended to the command line (only 3 or 4 build steps error out, so this isn't too tedious to do).

I also noticed that the binary I built would crash on my Core 2 Duo based system. I was running a simple "Hello World" JavaScript script. The same binary did not crash on a Haswell based system. Any idea why that would be? I am guessing that you may be using SSE 4 instructions? If so, is it possible to build ChakraCore to target only SSE 2?