Use dmlc-core as a cmake project

[apivovarov]

About the problem:
dmlc-core has cmake generated build_config.h which enables DMLC_LOG_STACK_TRACE in case cxxabi.h and execinfo.h files are present on the system. This feature (LOG_STACK_TRACE) is used in dmlc/logging.h which is used in tvm runtime/graph/graph_runtime.cc (via tvm/runtime/packed_func.h).

In order to build TVM runtime on a systems which do not have execinfo.h (e.g. OpenWRT) we should not automatically enable DMLC_LOG_STACK_TRACE.
This check will be done if we use dmlc-core as a cmake module.
Currently TVM build simply points to dmlc-core src and include folders but does not use dmlc-core cmake logic during the build.
Instead of that we should use dmlc-core as another cmake project.
For example xgboost already using dmlc-core as a cmake project

To verify that the fix works.

1. Rename /usr/include/execinfo.h to smth else
2. build tvm runtime.

cmake ..
make runtime

The build should work.

[tkonolige]

I've proposed this change in the past, but it seems like we want to use dmlc-core as a header only library. @tqchen can provide more info.

You'll be happy to know that #7153 move the stack trace code from dmlc-core into tvm proper. Maybe you should look at that PR?

[tqchen]

right, the dependency of TVM on dmlc-core is only limited to the header only, so we do not want to introduce a separate build dep step. Hopefully things can be easier after #7153