[llvm] [PowerPC] Support conversion between f16 and f128 (PR #130158)

[Alex Rønne Petersen via llvm-commits]

alexrp wrote:

FWIW, the backend crash that this is fixing affects Zig, so it would be great to backport this to 20.x if possible.

https://github.com/llvm/llvm-project/pull/130158