[llvm] [Offload] Add support for riscv64 to host plugin (PR #115773)

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joshua-arch1 wrote:

> Line 4228 in [0e3c791](/llvm/llvm-project/commit/0e3c791916a918cd2d7391ddb633fbe5faa00b86)

I'm sure that I have linked to libomp since I can see -lomp in the linking command. This undefined error stills exists after I added riscv64 to linkDevice.

https://github.com/llvm/llvm-project/pull/115773