[Metal] `firstbitlow.16`, `firstbitlow.64`, and `firstbithigh.64` fail with `gpu-exec: error: Failed to materializeAll.:` on Metal

[Icohedron]

The following tests fail with gpu-exec: error: Failed to materializeAll.: on Metal:

• test/Feature/HLSLLib/firstbitlow.16.test
• test/Feature/HLSLLib/firstbitlow.64.test
• test/Feature/HLSLLib/firstbithigh.64.test

As can be seen in the logs:

• https://github.com/llvm/offload-test-suite/actions/runs/19942216828/job/57182673499?pr=590
• https://github.com/llvm/offload-test-suite/actions/runs/19942216828/job/57182673462?pr=590