[llvm] Reland #118503: [Offload] Introduce offload-tblgen and initial new API implementation (PR #118614)

[Nikita Popov via llvm-commits]

nikic wrote:

Something problematic about how offload-tblgen is set up is that all of offload will (typically) be built as a runtime, while offload-tblgen is a host binary and depends on a host library. The compiler configuration used for the host compilation and the runtime build may be substantially different.

In our case it breaks because both compilers use different libstdc++ versions (more by accident than intention), but I'd expect this to also break if the built clang used for runtime builds is only configured for cross-compilation.

https://github.com/llvm/llvm-project/pull/118614