[clang] [Clang] Rework creating offloading toolchains (PR #125556)

[Joseph Huber via cfe-commits]

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@@ -109,65 +110,6 @@ using namespace clang::driver;
 using namespace clang;
 using namespace llvm::opt;
 
-static std::optional<llvm::Triple> getOffloadTargetTriple(const Driver &D,
-                                                          const ArgList &Args) {
-  auto OffloadTargets = Args.getAllArgValues(options::OPT_offload_EQ);
-  // Offload compilation flow does not support multiple targets for now. We
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jhuber6 wrote:

Yes, this unifies the OpenMP way of doing it. If you had some incredibly complex scenario it would look like this for OpenMP.
```
clang -fopenmp input.c --offload-targets=amdgcn-amd-amdhsa,nvptx64-nvidia-cuda,x86_64-unknown-linux-gnu -Xarch_amdgcn --offload-arch=gfx1030,gfx90a -Xarch_nvptx64 --offload-arch=sm_89 -Xarch_x86_64 --offload-arch=skylake
```
SYCL would work the same way, it would just create different toolchains due to the SYCL offloading kind.

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