s2 adds -std=c++11 uncoditonally

[ObiWahn]

https://github.com/google/s2geometry/blame/master/CMakeLists.txt#L61

You should add this flag for clang/gcc to the private target definitions only. Or better use set( CMAKE_CXX_STANDAD 11) / comple features . It could look like: target_compile_features(s2 PRIVATE cxx_std_11). Please use something newer than cmake 2.8.x. You have Blaze internally so don't force people to use antique cmake versions.