onnxruntime

Add SafeInt include to WinML targets (#3558)

Fixing Windows builds on the ort_training branch in preparation for the merge to master.
SafeInt (included via onnxruntime/core/common/safeint.h) was recently made a dependency of onnxruntime/core/framework/bfc_arena.h. That requires consumers of bfc_arena to compile with the SafeInt include directory.