[PATCH] [Zorg] Modify LibCxxAndABIBuilder to support testing libcxx with multiple standard versions.

[Dmitri Gribenko]

Could we add more targets instead, check-libcxx-cxx11, check-libcxx-cxx14 etc?

Then it would be easier to run them when developing libcxx itself.

http://reviews.llvm.org/D5114