[clang] [Clang][OpenCL] Fix Missing `-fdeclare-opencl-builtins` When Using `--save-temps` (PR #131017)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 approved this pull request.

Makes sense, though I don't know why we have a special flag for what is essentially a header.

https://github.com/llvm/llvm-project/pull/131017