- Remove compiler warnings whilst baking Metal source to binary
libraries, so true errors are easier to spot. Speeds up compilation,
with reduced STDOUT.
- Prevent invalid Metal libraries when baking to older target OSs,
which earlier MSL language support. In these cases, SPIRV-Cross
generates emulated atomic code via buffers (rather than images), that
isn't supported by Godot's Metal driver. These shaders are marked with
a new INVALID flag that triggers a recompilation on the device, by
signaling that the cache is invalid.