[clang] [CIR][X86] Implement convert_half builtins (PR #171615)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

> @andykaylor, the CI checks are failing and the build log is saying this-
> 
> `/home/gha/actions-runner/_work/llvm-project/llvm-project/clang/lib/CIR/CodeGen/CIRGenStmt.cpp:117:11: error: enumeration value 'DeferStmtClass' not handled in switch [-Werror,-Wswitch] 117 | switch (s->getStmtClass()) { | ^~~~~~~~~~~~~~~~~ 1 error generated. ninja: build stopped: cannot make progress due to previous errors.`
> 
> Neither did I edit this file nor does it contain `DeferStmtClass` in my local build. I rebased but still it's not there. I don't understand why is it happening.

`DeferStmtClass` was added by a change unrelated to CIR and since the CIR build is disabled by default, this issue wasn't caught in CI or by the buildbots. @badumbatish has fixed it here: https://github.com/llvm/llvm-project/pull/171773. If you rebase your PR, the CIR checks should work.

https://github.com/llvm/llvm-project/pull/171615