* Fix unsigned comparison and implicit double conversion

* Eliminate sign/unsigned compare warnings, implicit double conversion

* Missed type

* Neww int type

* omp compromise

* style

Restore DEFAULT_FLOAT_TOLERANCE_BITS logic in lrn, sigmoid, softmax. Should allow re-enabling PlaidML tests (#3277)

* Split backend_test.in.cpp

* style

* Move backend_{graph_comparison,mlir}.in.cpp back

* Move backend_mlir.in.cpp into backend/ dir

* Disable some tests in PlaidML manifest