[clang] [llvm] [Driver][RISC-V] Support YAML multilib config with selectRISCVMultilib fallback (PR #184973)

[Kito Cheng via cfe-commits]

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kito-cheng wrote:

The assumption here is we assume GCC and clang will using same default arch/abi/cmodel combination here, so in theory the default should be same, but that might not always true.

Few possible way here:
1) Probe GCC and extract the default multilib as a new variant of multilib, but that still cause problem if GCC and clang has different default arch/abi/cmodel.
2) Try to read the multilib to setting the default arch/abi/cmodel, but this might kind of overtake multilib config's responsibility


https://github.com/llvm/llvm-project/pull/184973