[clang] [Clang] Introduce '--offload-targets=' to genericall target toolchains (PR #125556)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

Contains two dependent commits, last one is the patch. Might need to have some additional error handling to reject known broken architectures, also need to correctly handle things like `--offload-targets=spirv64-amd-amdhsa,amdgcn-amd-amdhsa` in the new driver.

https://github.com/llvm/llvm-project/pull/125556