[clang] Correctly link and optimize device libraries with -mlink-builtin-bitcode (PR #69371)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> This handles the edge case where optimization introduces new device library functions, such as a fused sincos() from separate sin() and cos() calls.

This seems like a pretty big change to solve just this problem. Could we not just put `nobuiltin` on said function to stop it from doing that? Is this optimization explicitly valuable in this case?

https://github.com/llvm/llvm-project/pull/69371