[PATCH] [libcxx] Update the way the -std= flag is chosen by CMake and LibcxxTestFormat

[Eric Fiselier]

I don't think libc++ currently builds in C++03 mode anyway. I've tried building it with GCC 4.8 and Clang 3.4 with no version flag and both compilers fail to build future.cpp, hash.cpp and shared_mutex.cpp.

http://reviews.llvm.org/D4329