[clang] [clang] fix half && bfloat16 convert node expr codegen (PR #89051)

[Matt Arsenault via cfe-commits]

https://github.com/arsenm commented:

This appears to just assert today, but interpreting this as bitcast doesn't make sense. I would expect this to emit a pair of casts, fpext to float, and fptrunc down to half 

https://github.com/llvm/llvm-project/pull/89051