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

[Owen Anderson 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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resistor wrote:

Thank you for the suggestion! With a little fiddling that worked out nicely. PTAL.

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