Use stable outputs in illink targets (#64160)

Use stable outputs in illink targets (#64160)

* Use stable outputs in illink targets

While building locally multiple times, I noticed that the incremental build of the illink-targets are now to aggressive and could cause the targets to either never run or too often. This could be the case when the linker doesn't trim anything and copies the inputs to the outputs directory with preserving the timestamps. In such cases the inputs would always be newer than the outputs and the step would alway run. Also the path that was used to construct the outputs was missing a trailing directory separator. Using a marker file instead to not be dependent on the freshness of the linker output.