[llvm] [RISCV] Pick correct lround libcall for fp128 (PR #213220)

[Sam Elliott via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
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lenary wrote:

Can you do two separate commits: one to add a rv64 line to fp128.ll, and the second to fix this bug?

https://github.com/llvm/llvm-project/pull/213220