[llvm] [RISC-V] Pool duplicate scheduling class descriptors (PR #202659)

[David Zbarsky via llvm-commits]

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dzbarsky wrote:

yes, this pre-existing bit definitely caused some pain! I moved all offsets to `SchedClassNameOffsets` so these should be unified now, I think this is a lot nicer!

https://github.com/llvm/llvm-project/pull/202659