Platform keywords that only depend on current build target are treated as regular keywords and do not allow #pragma parameter selection.

1. Make an empty project (any pipe), standalone build target.
2. Go to project settings -> editor settings, turn Caching shader preprocessor on.
3. Add attched shader to the project. Create a cube and a new material, assign the material to the cube, assign the attached shader to the material.
4. Observe the cube is green.
5. Select the attached shader, observe two improt warnings.

Expected: no warnings, cube is red.