[mlir][gpu] Let gpu::TargetOptions carry LLVM library options (#242734)

ModuleToObject creates the LLVMContext and TargetMachine for GPU
serialization without a cl::LibraryOptionsContext, so its TargetMachine
reads NVPTX, AMDGPU, CodeGen, and MC options from T::Global. Since
#242689, only LLVMParseCommandLineOptions still sets T::Global, and
#242692 removes that.

Add gpu::TargetOptions::setLibraryOptions. The NVVM, ROCDL, and XeVM
serializers pass the context to ModuleToObject, which assigns it to its
LLVMContext and points its TargetMachine at it.

LLM-aided

GitOrigin-RevId: 0d99dea85f62f385cd90723e5ddbadd6ebd8accf