[llvm] [SPIRV] Support -fembed-bitcode=marker for non-shader modules (PR #162082)

[Juan Manuel Martinez Caamaño via llvm-commits]

jmmartinez wrote:

> Did you try simply deleting it and seeing what happens? What would be the cons of deleting it?

When`-fembed-bitcode=marker` is specified, I'm pretty sure that deleting the global could work; but I decided to preserve the global to respect what is expected from the option.

In the shader case, I'm leaning towards handling the bitcode-marker in the same way as for the kernel case.

I would have liked to have an `-fembed-bitcode=cmdline-only` option; but I prefer to not add yet-another-obscure-option that is exposed to the user. That's why I've settled to modify the backend instead.

https://github.com/llvm/llvm-project/pull/162082