cpp23: fix source so it compiles with c++23

[venik]

there are 2 changes:

1. A missing header was added to opensubdiv/bfr/tessellation.cpp. This header is missing due to new clang policy. see See https://libcxx.llvm.org/DesignDocs/HeaderRemovalPolicy.html. To prevent this in future _LIBCPP_REMOVE_TRANSITIVE_INCLUDES was added when OSD compiled with CLang.
2. ObjWriter::ObjWriter() ctor was fixed, since C++23 std::string doesnt accept nullptr. see (8) in https://en.cppreference.com/cpp/string/basic_string/basic_string.

TESTING:

cmake -B buildDir -D CMAKE_INSTALL_PREFIX=instDir -D CMAKE_CXX_STANDARD=23 -G Xcode -D NO_PTEX=1 -D NO_DOC=1 -D NO_OMP=1 -D NO_TBB=1 -D NO_CUDA=1 -D NO_OPENCL=1 -D NO_CLEW=1 -D "GLFW_LOCATION=/path/to/glfw" -S .
...
cmake --build buildDir --config Release --target install
...
** BUILD SUCCEEDED **

[davidgyu]

Filed as internal issue #OSD-480

[davidgyu]

Hi @venik Could you make sure that you have submitted a signed Contributing License Agreement Thanks!

[venik]

@davidgyu you already fixed most of it
6f7a62f

Need to find a printer to sign the paper, will do it over the weekends. Thanks