[clang] [HIP] Do not apply 'externally_initialized' to constant device variables (PR #182157)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> Can you be more specific? What case could be modified by something in the current IR?

Presumably it's because parts of the runtime will potentially touch these symbols while putting it on the GPU. I know in the Offload runtime we only read them but HIP might write some things.

https://github.com/llvm/llvm-project/pull/182157