[Bug target/108902] Conversions std::float16_t<->float with FP16C are not vectorized

[crazylht at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108902

--- Comment #4 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Hongtao.liu from comment #3)
> Yes,  in sse.md the corresponding expanders are only defined under
> TARGET_AVX512FP16.

Even w/ -mavx512fp16, it's still not vectorized since it relied on
vec_unpacks_hi/lo_v*hf for loop vectorizer. BB vectorizer seems ok.