fix NVTE_UB_WITH_MPI read (#1194)

* fix NVTE_UB_WITH_MPI read
Signed-off-by: Sangkug Lym <slym@nvidia.com>

* Add default value
Signed-off-by: Sangkug Lym <slym@nvidia.com>

---------
Signed-off-by: Sangkug Lym <slym@nvidia.com>
Co-authored-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

build_tools/pytorch.py

@@ -88,7 +88,7 @@ def setup_pytorch_extension(
     # Libraries
     library_dirs = []
     libraries = []
-    if os.getenv("NVTE_UB_WITH_MPI"):
+    if bool(int(os.getenv("NVTE_UB_WITH_MPI", 0))):
         assert (
             os.getenv("MPI_HOME") is not None
         ), "MPI_HOME must be set when compiling with NVTE_UB_WITH_MPI=1"