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

[Marshall Clow]

I'm fine with dropping the ability to build libc++ with a C++03 compiler.
[ I'm *not* fine with dropping the ability to use libc++ from c++03 code ]

Responsible opposing viewpoints... ?

http://reviews.llvm.org/D4329