The issue was caused by the fact that in this version
of MSVC unordered_map class is defined in <unordered_map>
header file, but this file declares the class int std::tr1
namespace.
This confused existing assumption that if there's an
existing <unordered_map> file then class is declared
in std namespace.
Added an extra check to CMake which detects whether
it's std or std::tr1 which actually contains class
of unordered_map.
This might be changed/cleaned in the future, for
now committing to our repository to solve compilation
error on windows.
Details of the patch in upstream can be found there:
https://ceres-solver-review.googlesource.com/#/c/4371/
b7bca8663a