[SYCL][NewOffloadModel] Support -fno-sycl-rdc with multiple SYCL target triples #23526

With the new offloading model, -fno-sycl-rdc only accepts SYCL targets of one triple. Several architectures of the same triple work (e.g. -fsycl-targets=intel_gpu_pvc,intel_gpu_dg2, after #23492), but mixing triples is rejected:

$ clang++ -fsycl --offload-new-driver -fsycl-targets=intel_gpu_pvc,spir64 -fno-sycl-rdc -c t.cpp
clang++: error: '-fno-sycl-rdc' is not supported with multiple SYCL offloading targets

The old offloading model accepts this:

$ clang++ -fsycl --no-offload-new-driver -fsycl-targets=intel_gpu_pvc,spir64_x86_64 -fno-sycl-rdc -c t.cpp

It finalizes each triple separately, running clang-offload-wrapper -target=spir64_gen and clang-offload-wrapper -target=spir64_x86_64, and bundles both results into the object.

Why the new model rejects it

• With -fno-sycl-rdc -c, each TU's device code is finalized by a single clang-linker-wrapper --no-sycl-rdc --emit-fatbin-only job, created for the whole packaged device code of the TU (clang/lib/Driver/Driver.cpp, the SYCLNoRDC branch that creates the LinkerWrapperJobAction).
• That job writes one offload wrapper module. Every image in a wrapper module is labeled with the arch name of one target triple (DeviceTargetSpec, e.g. spir64_gen), which the runtime uses to pick images for a device. So images of different triples can't share one module.
• The driver therefore rejects multiple SYCL targets for -fno-sycl-rdc (clang/lib/Driver/Driver.cpp, err_drv_sycl_no_rdc_multiple_targets); the comment there notes that the old offloading model supports this.

What's needed

Produce one wrapper module per triple in the -fno-sycl-rdc compile step and have the host compilation include all of them, then remove the driver restriction.