Fix a crash reported in #64331. The crash is described in the following
comment:
> It looks like the bug is being caused by the command line argument
--scf-parallel-loop-tiling=parallel-loop-tile-sizes=0. More
specifically, --scf-parallel-loop-tiling=parallel-loop-tile-sizes sets
the tileSize variable to 0 on [this
line](7cc1bfaf37/mlir/lib/Dialect/SCF/Transforms/ParallelLoopTiling.cpp (L67)).
tileSize is then used on [this
line](7cc1bfaf37/mlir/lib/Dialect/SCF/Transforms/ParallelLoopTiling.cpp (L117))
causing a divide by zero exception.
This PR will:
1. Call `signalPassFail()` when 0 is passed as a tile size.
2. Avoid the divide by zero that causes the crash.
Note: This is my first PR for MLIR, so please liberally critique it.
