[lld] [lld] Add infrastructure for handling RISCV vendor-specific relocations. (PR #159987)

[Jessica Clarke via llvm-commits]

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+# RUN: llvm-mc -triple riscv32 -mattr=+experimental-xqcibi,+xandesperf %s -filetype=obj -o %t.o
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jrtc27 wrote:

I’m not convinced this test makes much sense, in theory we should support all these relocations and then you wouldn’t be able to test this. Surely a better test would be to actually implement a vendor relocation?

https://github.com/llvm/llvm-project/pull/159987