[XRay][RISCV] RISCV support for XRay (#117368)

Add RISC-V support for XRay. The RV64 implementation has been tested in
both QEMU and in our hardware environment.

Currently this requires D and C

[XRay][RISCV] RISCV support for XRay (#117368)

Add RISC-V support for XRay. The RV64 implementation has been tested in
both QEMU and in our hardware environment.

Currently this requires D and C extensions, but since both RV64GC and
RVA22/RVA23 are becoming mainstream, I don't think this requirement will
be a big problem.

Based on the previous work by @a-poduval :
https://reviews.llvm.org/D117929

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Co-authored-by: Ashwin Poduval <ashwin.poduval@gmail.com>

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