[llvm] [SelectionDAG] Add `f16` soft promotion for `lrint` and `lround` (PR #152684)

[Trevor Gross via llvm-commits]

tgross35 wrote:

This doesn't actually seem to fix `l?lround` and strict ops, so I must be missing something still.

```text
Can't create an unknown libcall!
UNREACHABLE executed at /Users/tmgross/Documents/projects/llvm/llvm-project/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp:2201!
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and instructions to reproduce the bug.
Stack dump:
0.      Program arguments: /Users/tmgross/Documents/projects/llvm/llvm-build/bin/llc -mtriple=i686-unknown -mattr=sse2
1.      Running pass 'Function Pass Manager' on module '<stdin>'.
2.      Running pass 'X86 DAG->DAG Instruction Selection' on function '@test_lrint_i32_f16_strict'
```

https://github.com/llvm/llvm-project/pull/152684