Add private option to change build dialect from C++11
Add private option to change build dialect from C++11

Although libc++ only requires C++11 to build, there are other
reasons to turn on a newer dialect in the build. For example
IDE's may not highlight any C++14/C++17 in the headers when
configured for C++11. This patch add's a private option for
changing this.





git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@278638 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx