[RUNTIME] More reliable runtime only detection (#914)

* [RUNTIME] More reliable runtime only detection

* fix lint

python/tvm/_ffi/base.py

@@ -41,6 +41,10 @@ def _load_lib():
 __version__ = libinfo.__version__
 # library instance of nnvm
 _LIB, _LIB_NAME = _load_lib()
+
+# Whether we are runtime only
+_RUNTIME_ONLY = "runtime" in _LIB_NAME
+
 # The FFI mode of TVM
 _FFI_MODE = os.environ.get("TVM_FFI", "auto")
 

python/tvm/build_module.py

@@ -6,9 +6,9 @@ LoweredFunc and compiled Module.
 from __future__ import absolute_import as _abs
 import warnings
 import types
-import os
 
 from ._ffi.node import NodeBase, register_node
+from ._ffi.base import _RUNTIME_ONLY
 from . import api
 from . import tensor
 from . import schedule
@@ -226,7 +226,7 @@ def build_config(**kwargs):
             setattr(config, k, kwargs[k])
     return config
 
-if not os.environ.get("TVM_USE_RUNTIME_LIB", False):
+if not _RUNTIME_ONLY:
     # BuildConfig is not available in tvm_runtime
     BuildConfig.current = build_config()