Force CMAKE_CXX_STANDARD to 17 to override LLVM's mechanism. (#9924)
Force CMAKE_CXX_STANDARD to 17 to override LLVM's mechanism. (#9924)

This should work around a GCC bug that is causing multiple definition
errors when standards mismatch.
iree-org/iree,iree-org/iree,google/iree,google/iree,google/iree,google/iree,google/iree,iree-org/iree,iree-org/iree,iree-org/iree,iree-org/iree,google/iree,google/iree,iree-org/iree